问题补充:
---Don skate on the lake!
---Why not? Isn it thick enough?
A. to skate
B. skating on
C. skating
D. to skate on
答案:
A. to skate
B. skating on
C. skating
(答案→)D. to skate on
解析:句意:不要在湖上滑冰!为什么不行?冰还不够厚在上面滑冰吗?skate滑冰,滑冰是在湖上,还不定式to skate需要加一个介词on,表在冰上滑冰,故选D.