如图所示,小明在墙上挂2008年北京奥运会吉祥物“福娃”的宣传画时,用自制的重锤线来检查宣传画是否挂正,这是利用了重力的方向总是__________的特点。
竖直向下
—What ______ your mother do after work?
—She often ______ for us. [ ]
A. do, cook
B. does, cook
C. do, cooks
D. does, cooks
容易发生事故的阶段有哪些?