— You look scared. What happened?
— Well , I along the street the UFO landed.
A. was walking ; while
B. is walking ; when
C. was walking ; when
D. is walking ; while
网友回答
A. was walking ; while
B. is walking ; when
(答案→)C. was walking ; when
D. is walking ; while
解析：此题重点考查when和while引导的时间状语从句的基本区别。When引导的时间状语从句常用一般时态，有时也用进行时态；while引导的时间状语从句常用进行时态。