REFERENCES
1. Novoselov KS, Geim AK, Morozov SV, et al. Electric field effect in atomically thin carbon films. Science 2004;306:666-9.
2. Plechinger G, Castellanos-gomez A, Buscema M, et al. Control of biaxial strain in single-layer molybdenite using local thermal expansion of the substrate. 2D Mater 2015;2:015006.
3. Wang L, Nilsson ZN, Tahir M, Chen H, Sambur JB. Influence of the substrate on the optical and photo-electrochemical properties of monolayer MoS2. ACS Appl Mater Interfaces 2020;12:15034-42.
4. Jiang S, Xie H, Shan J, Mak KF. Exchange magnetostriction in two-dimensional antiferromagnets. Nat Mater 2020;19:1295-9.
5. Radisavljevic B, Radenovic A, Brivio J, Giacometti V, Kis A. Single-layer MoS2 transistors. Nat Nanotechnol 2011;6:147-50.
6. Yu H, Sun Q, Zhang T, Zhang X, Shen Y, Wang M. Is the strain responsible to instability of inorganic perovskites and their photovoltaic devices? Mater Today Energy 2021;19:100601.
7. Chen W, Zhang R, Sun Y, Wang J, Fan Y, Liu B. Preparation, properties, and electronic applications of 2D Bi2O2Se. Adv Powder Mater 2023;2:100080.
8. Yin Y, Kang X, Han B. Two-dimensional materials: synthesis and applications in the electro-reduction of carbon dioxide. Chem Synth 2022;2:19.
9. Chen L, Lin X, Dang W, Huang H, Liu G, Yang Z. Tantalum oxide nanosheets/polypropylene composite separator constructing lithium-ion channels for stable lithium metal batteries. Adv Compos Hybrid Mater 2023;6:12.
10. Liu C, Ye C, Wu Y, et al. Atomic-scale engineering of cation vacancies in two-dimensional unilamellar metal oxide nanosheets for electricity generation from water evaporation. Nano Energy 2023;110:108348.
11. Phalswal P, Khanna PK, Rubahn HG, Mishra YK. Nanostructured molybdenum dichalcogenides: a review. Mater Adv 2022;3:5672-97.
12. Zhang K, Feng S, Wang J, et al. Manganese doping of monolayer MoS2: the substrate is critical. Nano Lett 2015;15:6586-91.
13. Jin Y, Zeng Z, Xu Z, et al. Synthesis and transport properties of degenerate P-type Nb-doped WS2 monolayers. Chem Mater 2019;31:3534-41.
14. Li H, Du M, Mleczko MJ, et al. Kinetic study of hydrogen evolution reaction over strained MoS2 with sulfur vacancies using scanning electrochemical microscopy. J Am Chem Soc 2016;138:5123-9.
15. Liu C, Liu Y, Ma R, et al. Atomic cation-vacancy engineering of two-dimensional nanosheets for energy-related applications. Mater Chem Front 2023;7:1004-24.
16. Shao G, Lu Y, Hong J, et al. Seamlessly splicing metallic SnxMo1-xS2 at MoS2 edge for enhanced photoelectrocatalytic performance in microreactor. Adv Sci 2020;7:2002172.
17. Yang S, Liu F, Wu C, Yang S. Tuning surface properties of low dimensional materials via strain engineering. Small 2016;12:4028-47.
18. Zheng SW, Wang HY, Wang L, Luo Y, Gao BR, Sun HB. Observation of robust charge transfer under strain engineering in two-dimensional MoS2-WSe2 heterostructures. Nanoscale 2021;13:14081-8.
19. Miao Y, Zhao Y, Zhang S, Shi R, Zhang T. Strain engineering: a boosting strategy for photocatalysis. Adv Mater 2022;34:2200868.
20. Shaikh JS, Shaikh NS, Sabale S, et al. A phosphorus integrated strategy for supercapacitor: 2D black phosphorus-doped and phosphorus-doped materials. Mater Today Chem 2021;21:100480.
21. Yan Y, Ding S, Wu X, et al. Tuning the physical properties of ultrathin transition-metal dichalcogenides via strain engineering. RSC Adv 2020;10:39455-67.
22. Li H, Liu H, Zhou L, et al. Strain-tuning atomic substitution in two-dimensional atomic crystals. ACS Nano 2018;12:4853-60.
23. Bonavolontà C, Aramo C, Valentino M, et al. Graphene-polymer coating for the realization of strain sensors. Beilstein J Nanotechnol 2017;8:21-7.
24. Chaste J, Missaoui A, Huang S, et al. Intrinsic properties of suspended MoS2 on SiO2/Si pillar arrays for nanomechanics and optics. ACS Nano 2018;12:3235-42.
25. Wu Y, Wang L, Li H, Dong Q, Liu S. Strain of 2D materials via substrate engineering. Chin Chem Lett 2022;33:153-62.
26. Akinwande D, Brennan CJ, Bunch JS, et al. A review on mechanics and mechanical properties of 2D materials - Graphene and beyond. Extreme Mech Lett 2017;13:42-77.
27. Yang S, Chen Y, Jiang C. Strain engineering of two-dimensional materials: methods, properties, and applications. InfoMat 2021;3:397-420.
28. Hammer B, Nørskov JK. Theoretical surface science and catalysis - calculations and concepts. Adv Catal 2000;45:71-129.
29. Deng S, Sumant AV, Berry V. Strain engineering in two-dimensional nanomaterials beyond graphene. Nano Today 2018;22:14-35.
30. Zhou K, Dai K, Liu C, Shen C. Flexible conductive polymer composites for smart wearable strain sensors. SmartMat 2020;1:e1010.
31. Zhang H, Tersoff J, Xu S, et al. Approaching the ideal elastic strain limit in silicon nanowires. Sci Adv 2016;2:e1501382.
32. Mohiuddin TMG, Lombardo A, Nair RR, et al. Uniaxial strain in graphene by Raman spectroscopy: G peak splitting, Grüneisen parameters, and sample orientation. Phys Rev B 2009;79:205433.
33. Lu J, Gomes LC, Nunes RW, Castro Neto AH, Loh KP. Lattice relaxation at the interface of two-dimensional crystals: graphene and hexagonal boron-nitride. Nano Lett 2014;14:5133-9.
34. Li H, Contryman AW, Qian X, et al. Optoelectronic crystal of artificial atoms in strain-textured molybdenum disulphide. Nat Commun 2015;6:7381.
35. Azcatl A, Qin X, Prakash A, et al. Covalent nitrogen doping and compressive strain in MoS2 by remote N2 plasma exposure. Nano Lett 2016;16:5437-43.
36. Pierucci D, Henck H, Ben Aziza Z, et al. Tunable doping in hydrogenated single layered molybdenum disulfide. ACS Nano 2017;11:1755-61.
37. Hsu WT, Lu LS, Wang D, et al. Evidence of indirect gap in monolayer WSe2. Nat Commun 2017;8:929.
39. Li Z, Lv Y, Ren L, et al. Efficient strain modulation of 2D materials via polymer encapsulation. Nat Commun 2020;11:1151.
40. Lee CH, Khan A, Luo D, et al. Deep learning enabled strain mapping of single-atom defects in two-dimensional transition metal dichalcogenides with sub-picometer precision. Nano Lett 2020;20:3369-77.
41. Li L, Schultz JF, Mahapatra S, et al. Angstrom-scale spectroscopic visualization of interfacial interactions in an organic/borophene vertical heterostructure. J Am Chem Soc 2021;143:15624-34.
42. Wu G, Han X, Cai J, et al. In-plane strain engineering in ultrathin noble metal nanosheets boosts the intrinsic electrocatalytic hydrogen evolution activity. Nat Commun 2022;13:4200.
43. Cao X, Huang A, Liang C, et al. Engineering lattice disorder on a photocatalyst: photochromic BiOBr nanosheets enhance activation of aromatic C-H bonds via water oxidation. J Am Chem Soc 2022;144:3386-97.
44. Bhatt MD, Lee JS. Effect of lattice strain on nanomaterials in energy applications: a perspective on experiment and theory. Int J Hydrog Energy 2017;42:16064-107.
45. Sharma SK, Sharma G, Gaur A, et al. Progress in electrode and electrolyte materials: path to all-solid-state Li-ion batteries. Energy Adv 2022;1:457-510.
46. Xu X, Liang T, Kong D, Wang B, Zhi L. Strain engineering of two-dimensional materials for advanced electrocatalysts. Mater Today Nano 2021;14:100111.
47. Khorshidi A, Violet J, Hashemi J, Peterson AA. How strain can break the scaling relations of catalysis. Nat Catal 2018;1:263-8.
48. Deeksha, Kour P, Ahmed I, et al. Transition metal-based perovskite oxides: emerging electrocatalysts for oxygen evolution reaction. ChemCatChem 2023;15:e202300040.
49. Dalrymple OK, Stefanakos E, Trotz MA, Goswami DY. A review of the mechanisms and modeling of photocatalytic disinfection. Appl Catal B Environ 2010;98:27-38.
50. Jiang J, Pendse S, Zhang L, Shi J. Strain related new sciences and devices in low-dimensional binary oxides. Nano Energy 2022;104:107917.
51. Xu Y, von Delius M. The supramolecular chemistry of strained carbon nanohoops. Angew Chem Int Ed Engl 2020;59:559-73.
52. Lloyd D, Liu X, Christopher JW, et al. Band gap engineering with ultralarge biaxial strains in suspended monolayer MoS2. Nano Lett 2016;16:5836-41.
53. Liu B, Liao Q, Zhang X, et al. Strain-engineered van der waals interfaces of mixed-dimensional heterostructure arrays. ACS Nano 2019;13:9057-66.
54. Conley HJ, Wang B, Ziegler JI, Haglund RF Jr, Pantelides ST, Bolotin KI. Bandgap engineering of strained monolayer and bilayer MoS2. Nano Lett 2013;13:3626-30.
55. Di J, Song P, Zhu C, et al. Strain-engineering of Bi12 O17 Br2 nanotubes for boosting photocatalytic CO2 reduction. ACS Mater Lett 2020;2:1025-32.
56. Feng H, Xu Z, Wang L, et al. Modulation of photocatalytic properties by strain in 2D BiOBr nanosheets. ACS Appl Mater Interfaces 2015;7:27592-6.
57. Franchini IR, Bertoni G, Falqui A, Giannini C, Wang LW, Manna L. Colloidal PbTe-aunanocrystal heterostructures. J Mater Chem 2010;20:1357-66.
58. Zhang P, Cheng N, Li M, et al. Transition-metal substitution-induced lattice strain and electrical polarity reversal in monolayer WS2. ACS Appl Mater Interfaces 2020;12:18650-9.
59. Castellanos-Gomez A, Roldán R, Cappelluti E, et al. Local strain engineering in atomically thin MoS2. Nano Lett 2013;13:5361-6.
60. Ni W, Wang T, Schouwink PA, Chuang YC, Chen HM, Hu X. Efficient hydrogen oxidation catalyzed by strain-engineered nickel nanoparticles. Angew Chem Int Ed Engl 2020;59:10797-801.
61. Chattot R, Le Bacq O, Beermann V, et al. Surface distortion as a unifying concept and descriptor in oxygen reduction reaction electrocatalysis. Nat Mater 2018;17:827-33.
62. Liu Y, Zeng C, Zhong J, Ding J, Wang ZM, Liu Z. Spintronics in two-dimensional materials. Nanomicro Lett 2020;12:93.
63. Bai S, Zhang N, Gao C, Xiong Y. Defect engineering in photocatalytic materials. Nano Energy 2018;53:296-336.
64. Wang S, Wang L, Xie L, et al. Dislocation-strained MoS2 nanosheets for high-efficiency hydrogen evolution reaction. Nano Res 2022;15:4996-5003.
65. Mao Q, Deng K, Wang W, et al. N-doping induced lattice-strained porous PdIr bimetallene for pH-universal hydrogen evolution electrocatalysis. J Mater Chem A 2022;10:8364-70.
66. Zhu Y, Yang H, Sun F, Wang X. Controllable Growth of Ultrathin P-doped ZnO Nanosheets. Nanoscale Res Lett 2016;11:175.
67. Liang S, Han B, Ou X, et al. Lattice-strained nickel hydroxide nanosheets for the boosted diluted CO2 photoreduction. Environ Sci Nano 2021;8:2360-71.
68. Zhao Y, Zhao Y, Waterhouse GIN, et al. Photocatalysts: layered-double-hydroxide nanosheets as efficient visible-light-driven photocatalysts for dinitrogen fixation (Adv. Mater. 42/2017). Adv Mater 2017;29:1703828.
69. Zhang W, Cai L, Cao S, et al. Electrode materials: interfacial lattice-strain-driven generation of oxygen vacancies in an aerobic-annealed TiO2(B) electrode (Adv. Mater. 52/2019). Adv Mater 2019;31:1970367.
70. Choi SY, Kim SD, Choi M, et al. Assessment of strain-generated oxygen vacancies using SrTiO3 bicrystals. Nano Lett 2015;15:4129-34.
71. Li H, Tsai C, Koh AL, et al. Correction: corrigendum: activating and optimizing MoS2 basal planes for hydrogen evolution through the formation of strained sulphur vacancies. Nat Mater 2016;15:364.
72. Zhao Y, Zhao Y, Shi R, et al. Tuning oxygen vacancies in ultrathin TiO2 Nanosheets to boost photocatalytic nitrogen fixation up to 700 nm. Adv Mater 2019;31:1806482.
73. Jeong HY, Jin Y, Yun SJ, et al. Heterogeneous defect domains in single-crystalline hexagonal WS2. Adv Mater 2017;29:1605043.
74. Luo M, Guo S. Strain-controlled electrocatalysis on multimetallic nanomaterials. Nat Rev Mater 2017;2:17059.
75. Lemme MC, Akinwande D, Huyghebaert C, Stampfer C. 2D materials for future heterogeneous electronics. Nat Commun 2022;13:1392.
76. Li MY, Shi Y, Cheng CC, et al. Epitaxial growth of a monolayer WSe2-MoS2 lateral p-n junction with an atomically sharp interface. Science 2015;349:524-8.
77. Xie S, Tu L, Han Y, et al. Coherent, atomically thin transition-metal dichalcogenide superlattices with engineered strain. Science 2018;359:1131-6.
78. Zhu Z, Svensson J, Persson AR, Wallenberg R, Gromov AV, Wernersson LE. Compressively-strained GaSb nanowires with core-shell heterostructures. Nano Res 2020;13:2517-24.
79. Zhang C, Li MY, Tersoff J, et al. Strain distributions and their influence on electronic structures of WSe2-MoS2 laterally strained heterojunctions. Nat Nanotechnol 2018;13:152-8.
80. Xiong P, Zhang F, Zhang X, et al. Strain engineering of two-dimensional multilayered heterostructures for beyond-lithium-based rechargeable batteries. Nat Commun 2020;11:3297.
81. Zhang Z, Chen P, Duan X, Zang K, Luo J, Duan X. Robust epitaxial growth of two-dimensional heterostructures, multiheterostructures, and superlattices. Science 2017;357:788-92.
82. He K, Poole C, Mak KF, Shan J. Experimental demonstration of continuous electronic structure tuning via strain in atomically thin MoS2. Nano Lett 2013;13:2931-6.
83. Ni ZH, Yu T, Lu YH, Wang YY, Feng YP, Shen ZX. Uniaxial strain on graphene: Raman spectroscopy study and band-gap opening. ACS Nano 2008;2:2301-5.
84. Zhang Q, Chang Z, Xu G, et al. Strain relaxation of monolayer WS2 on plastic substrate. Adv Funct Mater 2016;26:8707-14.
85. Huang M, Yan H, Chen C, Song D, Heinz TF, Hone J. Phonon softening and crystallographic orientation of strained graphene studied by Raman spectroscopy. Proc Natl Acad Sci U S A 2009;106:7304-8.
86. Hui YY, Liu X, Jie W, et al. Exceptional tunability of band energy in a compressively strained trilayer MoS2 sheet. ACS Nano 2013;7:7126-31.
87. Zeng M, Liu J, Zhou L, et al. Bandgap tuning of two-dimensional materials by sphere diameter engineering. Nat Mater 2020;19:528-33.
88. Zong Z, Chen CL, Dokmeci MR, Wan K. Direct measurement of graphene adhesion on silicon surface by intercalation of nanoparticles. J Appl Phys 2010;107:026104.
89. Lee JK, Yamazaki S, Yun H, et al. Modification of electrical properties of graphene by substrate-induced nanomodulation. Nano Lett 2013;13:3494-500.
90. Zhang Y, Heiranian M, Janicek B, et al. Strain modulation of graphene by nanoscale substrate curvatures: a molecular view. Nano Lett 2018;18:2098-104.
91. Reserbat-Plantey A, Kalita D, Han Z, et al. Strain superlattices and macroscale suspension of graphene induced by corrugated substrates. Nano Lett 2014;14:5044-51.
92. Lloyd D, Liu X, Boddeti N, et al. Adhesion, stiffness, and instability in atomically thin MoS2 bubbles. Nano Lett 2017;17:5329-34.
93. Tomori H, Kanda A, Goto H, et al. Introducing nonuniform strain to graphene using dielectric nanopillars. Appl Phys Express 2011;4:075102.
94. Cai W, Wang J, He Y, et al. Strain-modulated photoelectric responses from a flexible α-In2Se3/3R MoS2 heterojunction. Nanomicro Lett 2021;13:74.
95. Liu Z, Zhu T, Wang J, et al. Functionalized fiber-based strain sensors: pathway to next-generation wearable electronics. Nanomicro Lett 2022;14:61.
96. Zhang CY, Zhang C, Pan JL, et al. Surface strain-enhanced MoS2 as a high-performance cathode catalyst for lithium-sulfur batteries. eScience 2022;2:405-15.
97. Liu Z, Liu C, Chen Z, et al. Recent advances in two-dimensional materials for hydrovoltaic energy technology. Exploration 2023;3:20220061.
98. Xiong P, Zhang F, Zhang X, et al. Atomic-scale regulation of anionic and cationic migration in alkali metal batteries. Nat Commun 2021;12:4184.
99. Xiong P, Wu Y, Liu Y, et al. Two-dimensional organic-inorganic superlattice-like heterostructures for energy storage applications. Energy Environ Sci 2020;13:4834-53.
100. Jiang K, Xiong P, Ji J, et al. Two-dimensional molecular sheets of transition metal oxides toward wearable energy storage. Acc Chem Res 2020;53:2443-55.
101. Dai Z, Liu L, Zhang Z. 2D materials: strain engineering of 2D materials: issues and opportunities at the interface (Adv. Mater. 45/2019). Adv Mater 2019;31:1970322.
102. Ma Y, Jang KI, Wang L, et al. Design of strain-limiting substrate materials for stretchable and flexible electronics. Adv Funct Mater 2016;26:5345-51.
103. Li F, Shen T, Wang C, Zhang Y, Qi J, Zhang H. Recent advances in strain-induced piezoelectric and piezoresistive effect-engineered 2D semiconductors for adaptive electronics and optoelectronics. Nanomicro Lett 2020;12:106.
104. Xiong P, Ma R, Wang G, Sasaki T. Progress and perspective on two-dimensional unilamellar metal oxide nanosheets and tailored nanostructures from them for electrochemical energy storage. Energy Storage Mater 2019;19:281-98.
105. Hao J, Zheng J, Ling F, et al. Strain-engineered two-dimensional MoS2 as anode material for performance enhancement of Li/Na-ion batteries. Sci Rep 2018;8:2079.
106. Oakes L, Carter R, Hanken T, et al. Interface strain in vertically stacked two-dimensional heterostructured carbon-MoS2 nanosheets controls electrochemical reactivity. Nat Commun 2016;7:11796.
107. Ma M, Zhang S, Wang L, et al. Harnessing the volume expansion of MoS3 anode by structure engineering to achieve high performance beyond lithium-based rechargeable batteries. Adv Mater 2021;33:2106232.
108. Liu Y, Ding C, Yan X, et al. Interface-strain-confined synthesis of amorphous TiO2 mesoporous nanosheets with stable pseudocapacitive lithium storage. Chem Eng J 2021;420:129894.
109. Liu MC, Zhang BM, Zhang YS, et al. Regulating interlayer spacing with pillar and strain structures in Ti3C2 MXene layers by molecular welding for superior alkali metal ion storage. Mater Today Energy 2021;22:100832.
110. Chen S, Fu Z, Zhang H, et al. Surface electrochemical stability and strain-tunable lithium storage of highly flexible 2D transition metal carbides. Adv Funct Mater 2018;28:1804867.
112. Sun Y, Liu Q, Gao S, et al. Pits confined in ultrathin cerium(IV) oxide for studying catalytic centers in carbon monoxide oxidation. Nat Commun 2013;4:2899.
113. Bahadoran A, Ramakrishna S, Masudy-panah S, et al. Rational construction of a 0D/1D S-scheme CeO2/CdWO4 heterojunction for photocatalytic CO2 reduction and H2 production. Ind Eng Chem Res 2022;61:10931-44.
114. Bhawna, Kumar S, Sharma R, et al. Catalytic heterostructured materials for CO2 mitigation and conversion into fuels: a renewable energy approach towards a sustainable environment. Sustain Energy Fuels 2023;7:4354-95.
115. Liu G, Zhen C, Kang Y, Wang L, Cheng HM. Unique physicochemical properties of two-dimensional light absorbers facilitating photocatalysis. Chem Soc Rev 2018;47:6410-44.
116. Biele R, Flores E, Ares JR, et al. Strain-induced band gap engineering in layered TiS3. Nano Res 2018;11:225-32.
117. Feng J, Qian X, Huang CW, Li J. Strain-engineered artificial atom as a broad-spectrum solar energy funnel. Nature Photon 2012;6:866-72.
118. Pak S, Lee J, Lee YW, et al. Strain-mediated interlayer coupling effects on the excitonic behaviors in an epitaxially grown MoS2/WS2 van der Waals heterobilayer. Nano Lett 2017;17:5634-40.
119. Wang SL, Luo X, Zhou X, et al. Fabrication and properties of a free-standing two-dimensional titania. J Am Chem Soc 2017;139:15414-9.
120. Tao J, Wang X, Xu M, Liu C, Ge J, Xing W. Non-noble metals as activity sites for ORR catalysts in proton exchange membrane fuel cells (PEMFCs). Ind Chem Mater 2023;1:388-409.
121. Mirshokraee SA, Muhyuddin M, Orsilli J, et al. Mono-, bi- and tri-metallic platinum group metal-free electrocatalysts for hydrogen evolution reaction following a facile synthetic route. Ind Chem Mater 2023;1:343-59.
122. Wang H, Wang L, Luo Q, et al. Two-dimensional manganese oxide on ceria for the catalytic partial oxidation of hydrocarbons. Chem Synth 2022;2:2.
123. He Y, Kang Z, Li J, Li Y, Tian X. Recent progress of manganese dioxide based electrocatalysts for the oxygen evolution reaction. Ind Chem Mater 2023;1:312-31.
124. Chang CC, Chen CC, Hung WH, Hsu IK-, Pimenta MA, Cronin SB. Strain-induced D band observed in carbon nanotubes. Nano Res 2012;5:854-62.
125. Qian X, Fu L, Li J. Topological crystalline insulator nanomembrane with strain-tunable band gap. Nano Res 2015;8:967-79.
126. Qiu Y, Rao Y, Zheng Y, Hu H, Zhang W, Guo X. Activating ruthenium dioxide via compressive strain achieving efficient multifunctional electrocatalysis for Zn-air batteries and overall water splitting. InfoMat 2022;4:e12326.
127. Zhao W, Kozlov SM, Höfert O, et al. Graphene on Ni(111): coexistence of different surface structures. J Phys Chem Lett 2011;2:759-64.
128. You B, Tang MT, Tsai C, Abild-Pedersen F, Zheng X, Li H. Enhancing electrocatalytic water splitting by strain engineering. Adv Mater 2019;31:1807001.
129. Mao X, Qin Z, Ge S, Rong C, Zhang B, Xuan F. Strain engineering of electrocatalysts for hydrogen evolution reaction. Mater Horiz 2023;10:340-60.
130. Voiry D, Yamaguchi H, Li J, et al. Enhanced catalytic activity in strained chemically exfoliated WS2 nanosheets for hydrogen evolution. Nat Mater 2013;12:850-5.
131. Hwang DY, Choi KH, Park JE, Suh DH. Highly efficient hydrogen evolution reaction by strain and phase engineering in composites of Pt and MoS2 nano-scrolls. Phys Chem Chem Phys 2017;19:18356-65.
132. Tan Y, Liu P, Chen L, et al. Monolayer MoS2 films supported by 3D nanoporous metals for high-efficiency electrocatalytic hydrogen production. Adv Mater 2014;26:8023-8.
133. Lee JH, Jang WS, Han SW, Baik HK. Efficient hydrogen evolution by mechanically strained MoS2 nanosheets. Langmuir 2014;30:9866-73.
