--- Did you turn off the lights before you left the computer room? ---- Oh I forget them

问题补充：

--- Did you turn off the lights before you left the computer room?

---- Oh, I forget them off. I’ll go to do it.

A. to turn

B. having been turned

C. to have turned

D. turning

答案：

(答案→)A. to turn

B. having been turned

C. to have turned

D. turning

解析：考查forget的用法。“你离开电脑室前关灯了吗？”“噢，我忘记关了。我现在就去关。”forget to do sth.“忘记要做某事”；forget doing sth.“忘记做过某事”。根据答语可知，没有做关灯这个动作，故加不定式，排除B、D；A项表示未做。故选A。