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。