Don’t forgetthe lights when you leave.A. to turn onB. turn onC. to turn offD. turning off

问题补充：

Don’t forgetthe lights when you leave.

A. to turn on

B. turn on

C. to turn off

D. turning off

答案：

A. to turn on

B. turn on

(答案→)C. to turn off

D. turning off

解析：本题的含义是当你离开的时候不要忘记关灯，turn off表示关上的意思，forget to do表示忘记未做的事，故本题选C。