问题补充：
I can’t decide .
A. to buy which one
B. which one to buy
C. to buy which
D. which to buy one
答案：
A. to buy which one
(答案→)B. which one to buy
C. to buy which
D. which to buy one
解析：句意：我不能决定买哪一个。本题考查不定式。特殊疑问词后跟to do。而which意为“哪一个”，相当于形容词，所以which后应加one。根据题意，故选B。
