问题补充:
While along the road, Mr. Smith met an old friend of his.
A. walked
B. he is walking
C. walking
D. is walking
答案:
A. walked
B. he is walking
(答案→)C. walking
D. is walking
解析:考查状语从句及其省略。句子可还原成由while引导的时间状语从句,While he was walking along the road, Mr. Smith met an old friend of his.故B错误在is应改成was。状语从句的省略是指省略从句的主语和部分谓语,即省略he was,故选C