Question

I met Mr. Green ________ I was walking across the bridge, but I didn't say hello to him.

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

Answer 1

D
解析：本题考查时间状语从句的用法。before意为“在……之前”；after意为“在……之后”；until意为“直到……”；while意为“与……的同时”。从句意知道while符合句子的意思。因此D为正确答案。