单项选择题
A.19.6kN/m2 B.19.3kN/m2 C.19.5kN/m2 D.20.9kN/m2
A.539mm2 B.841mm2 C.1143mm2 D.1257mm2
A.12.4kN/m2 B.12.0kN/m2 C.12.8kN/m2 D.13.5kN/m2