单项选择题
A.2m B.3m C.4m D.5m
A.1.5m B.2.0m C.2.5mm D.3.0m
A.5~10mm厚水泥浆 B.5~10mm厚水泥砂浆 C.50~100mm厚水泥砂浆 D.500mm厚石子增加一倍的混凝土