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

问题补充：

until the lights have turned to green.

A. Wait

B. To wait

C. Waiting

D. Having waited

答案：

(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。