until the lights have turned to green. A. WaitB. To waitC. WaitingD. Having waited

网友回答

(答案→)A. Wait
B. To wait
C. Waiting
D. Having waited
解析：考查动词。本题考查祈使句，原因是每句中均包括有从属连词(如 when, before, until 等)，即整个句子为一个主从复合句，而所填空句仍为祈使句。故选A。句意：等待直到所有的灯都变绿。