A.1/300 B.1/400 C.1/500 D.1/600
A.一 B.二 C.三 D.四
A.750V B.500V C.250V D.50V
A.8cm B.10cm C.12cm D.14cm
A.0.7kN/m2 B.0.6kN/m2 C.0.5kN/m2 D.0.4kN/m2