Tom didn’t understand the text the teacher explained it to him.A. whenB. whileC. untilD.

问题补充：

Tom didn’t understand the text the teacher explained it to him.

A. when

B. while

C. until

D. since

答案：

A. when

B. while

(答案→)C. until

D. since

解析：本题引导的是一个时间状语从句，not……until表示直到……才的意思，本题的含义直到老师给汤姆解释了文章，汤姆才弄懂，故选C。