A.15 B.20 C.25 D.30
A.層高不大于5m時為6mm,層高大于5m時為8mm B.層高不大于5m時為8mm,層高大于5m時為6mm C.層高不大于5m時為7mm,層高大于5m時為5mm D.層高不大于5m時為5mm,層高大于5m時為7mm
A.3 B.4 C.5 D.6