Every evening the students go to bed at 10:30 and the lights are turned off.A. at onceB. o

问题补充：

Every evening the students go to bed at 10:30 and the lights are turned off.

A. at once

B. on purpose

C. at present

D. as usual

答案：

A. at once

B. on purpose

C. at present

(答案→)D. as usual

解析：介词短语辨析。A立刻，马上；B故意；C目前，现在；D和平时一样；句意：每天晚上学生都和平时一样在10点30睡觉，灯光就在那个时候被熄灭。故D正确。