问题补充:
—Hey, man. You can’t cross the street now. You have to wait the traffic turn green.
—Oh, sorry and thank you.
A. when
B. after
C. until
D. while
答案:
A. when
B. after
(答案→)C. until
D. while
解析:A项在……的时候;B项在……之后;C项到……为止,在……以前;D项当……的时候。句意“嘿,伙计。现在你不能穿过街道。在交通灯变绿以前,你必须等。C项符合题意。