问题补充：
Please make sure all the lights are before you go to bed.
A. turned on
B. turned down
C. switched off
D. switched on
答案：
A. turned on
B. turned down
(答案→)C. switched off
D. switched on
解析： 短语辨析。 A.打开 B.减小；调低 C.关掉；切断电源 D. 开启。句意：请确认在你睡觉前所有的灯都被关掉了。这里强调是关掉电源。故选C。
