He left the key he had been an hour before.A. whatB. thatC. whereD. which

问题补充：

He left the key he had been an hour before.

A. what

B. that

C. where

D. which

答案：

A. what

B. that

(答案→)C. where

D. which

解析：考查状语从句。句意：他把钥匙忘记在了一小时前他所在的地方。本句中的where he had been an hour before在句中做地点状语，修饰动词left the key。故C正确。