Have you visited the theater built on ________ used to be a temple?

Have you visited the theater built on ________ used to be a temple?

A.where

B.that

C.what

D.when

答案及解析： C

解析：

what引导on的宾语从句，并在从句中作主语。容易错选A项，where是副词，不能充当主语或宾语。