土坝地基开挖与清理的对象有（）。
A.大面积且较厚的砂砾石层
B.蛮石
C.有机质
D.少量淤泥
E.局部少量砂砾石
参考答案：B, C, D, E
He ______ go out with his parents, but now he ______ staying at home alone.[ ]
A. used to, is used to
B. is used to, used to
C. use to, is used to
试述人体运动系统的组成？
