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

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.then

答案及解析： A

解析：

the first of which属于“介词+关系代词”结构引导的定语从句。