While the boy down the street the UFO .A. was walking; was landingB. walked; landedC.

问题补充：

While the boy down the street, the UFO .

A. was walking; was landing

B. walked; landed

C. was walking; landed

D. walked; was landing

答案：

A. was walking; was landing

B. walked; landed

(答案→)C. was walking; landed

D. walked; was landing

解析：根据语境可知此句的含义是这个小男孩沿着街道走的时候，ufo正在着陆。此题重点考查的是while引导的状语从句表示当…的时候。其强调的是两个动作同时进行，并且经常用进行时态，故选C。