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
网友回答
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。