It suddenly occurred to me I hadn’t locked my doorA. whichB. whereC. thatD. whether

问题补充：

It suddenly occurred to me I hadn’t locked my door．

A. which

B. where

C. that

D. whether

答案：

A. which

B. where

(答案→)C. that

D. whether

解析：句意：我突然想起我没有锁门。这里使用了固定句型“It occurred to sb that…”，某人突然想起…，that引导主语从句，it是形式主语，所以选C。