例题1.
Ann is so careful that she always goes over her exercises to ______there are no mistakes.
A. look for B. make sure C. find out D. think about
【解析】make sure是固定词组，意思是“确信”，她检查自己作业的目的是确信不犯错误。
例题2.
--- Which of the two English dictionaries will you buy ?
--- Ill buy ______ of them, so I can give one to my friend, Hellen.
A. either B. neither C. all D. both
【解析】选D。从so 引导的结果状语从句可判断一个字典给自己，另一个给朋友Hellen, 因此可知买两本英语字典，其中both表示“两者都”。
例题3.
He ______ two thousand trees since 1985.
A. plants B. planted C. will plant D. has planted
【解析】since意为自从……以来，应与现在完成式连用，故选D。