单项选择题
A.500g/m2 B.300g/m3 C.400g/cm2 D.600g/m2
A.前进向上,自重切土 B.后退向下,自重切土 C.前进向上,强制切土 D.后退向下,强制切土
A.20~30mm B.50~100mm C.60~80mm D.40~50mm