This is the best book I have been looking for all this year.A. whoB. whomC. whichD. /

问题补充：

This is the best book I have been looking for all this year.

A. who

B. whom

C. which

D. /

答案：

A. who

B. whom

C. which

(答案→)D. /

解析：考察定语从句。先行词是指物的名词且前面有形容词最高级修饰的时候，后面的关系代词使用That，本句中的that充当宾语，可以省略，故D正确。