I had to buy ________ these books because I didn't know which one is the best．

I had to buy ________ these books because I didn't know which one is the best．

A.both

B.none

C.neither

D.all

答案及解析： D

解析：

由句中…is the best推知不是两本书，而是两本以上，再据句意可知选D。