单项选择题
A.1429mm2 B.1571mm2 C.1026mm2 D.624mm2
A.19.6kN/m2 B.19.3kN/m2 C.19.5kN/m2 D.20.9kN/m2
A.539mm2 B.841mm2 C.1143mm2 D.1257mm2