A.50kN/m2 B.60kN/m2 C.70kN/m2 D.87kN/m2
A.20%~40% B.40%~60% C.30%~50% D.50%~70%
A.等于50kN/m2 B.大于50kN/m2 C.小于50kN/m2 D.小于或等于50kN/m2