Question

---Hurry up. The bus is coming.

---Oh, no. We mustn't cross the street ________ the traffic lights are green.

1. A.
   after
2. B.
   since
3. C.
   while
4. D.
   until

Answer 1

D
本题考查了从属连词的用法。After意思是“在……之后”；since意思是“自……以来”；while意思是“当……的时候”。分析句意排除A、B、C三项。D项构成“not... until”结构。故选D。