While for the bus, I happened to e across my childhood friend, Tom.
A. waited
B. wait
C. waiting
D. to wait
网友回答
A. waited
B. wait
(答案→)C. waiting
D. to wait
解析：考查状语从句的省略式，当主从句的主语一致时，要省略从句的主语和be动词，while waiting=while I was waiting，句意：当我在等公共汽车的时候，碰巧遇到儿时的朋友，汤姆。选C。