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：考查时态：句意：当男孩正沿着街道走的时候，不明飞行物着陆了，while引导的时间状语从句经常用过去进行时态。主句用一般过去时，选C。