问题补充：
The two dresses are very nice. I can’t decide 。
A. which one should I buy
B. which one to buy
C. which one I to buy
D. which I bought one
答案：
A. which one should I buy
(答案→)B. which one to buy
C. which one I to buy
D. which I bought one
解析：考察特殊疑问词的用法。特殊疑问词+to do sth句意：这两条裙子都很漂亮，我不能决定买哪一条。故选B
