It is said that this is the biggest lab they have ever built in their school. A. whichB.

问题补充：

It is said that this is the biggest lab they have ever built in their school.

A. which

B. what

C. 不填

D. where

答案：

A. which

B. what

(答案→)C. 不填

D. where

解析：考查定语从句。当表示事物的先行词前面有最高级修饰的时候，使用关系代词that,当关系代词在句子做宾语的时候，又可以省略。本题的that指代前面的先行词the biggest lab，在句中做built的宾语，可以省略。