He met many problems he was going over his lessons.A. beforeB. as soon asC. sinceD. while

问题补充：

He met many problems he was going over his lessons.

A. before

B. as soon as

C. since

D. while

答案：

A. before

B. as soon as

C. since

(答案→)D. while

解析：翻译：当他正在复习他的功课时他遇见了很多困难

A在。。。。之前

B一。。。。就

C自从

D当。。。。时

故选D