for the bus I heard a noise A. While waitingB. While I waitingC. I was waitingD. Waited

问题补充：

for the bus, I heard a noise,

A. While waiting

B. While I waiting

C. I was waiting

D. Waited

答案：

(答案→)A. While waiting

B. While I waiting

C. I was waiting

D. Waited

解析：考查状语从句的省略式，英语中的主从句的主语一致时，可以省略从句的主语和be动词，while waiting=while I was waiting，句意是：当我等汽车的时候，我听到一生噪音。选A。