This is the third book that he has written in the past five years the first of I really e

问题补充：

This is the third book that he has written in the past five years, the first of I really enjoyed.

A. which

B. that

C. those

D. them

答案：

(答案→)A. which

B. that

C. those

D. them

解析：考查定语从句：句意：这是他在过去5年里面写的第三本书，我真的喜欢其中的第一本。这是由名词+of+关系代词构成的定语从句，修饰先行词book，所以选A。