上升器用做上升过程中（）。
A.可以自由在绳索上移动
B.仅能在绳索上向下移动
C.仅能在绳索上向上移动
D.能起到固定和保护作用
参考答案：C, D
—Where is Jack, please?
—He _____ be in the reading room. [ ]
A. need
B. shall
C. must
D. would
Please ______ the lights before you leave the classroom. [ ]
A. turn down
B. turn on
C. turn off
D. turn up
