单项选择题
A.30N/cm2 B.25N/cm2 C.20N/cm2 D.35N/cm2
A.1400,4.5 B.1370,5.5 C.1370,4.5 D.1400,5.5
A.1900,9.6 B.1800, 9.6 C.1900,8.0 D.1950,9.6