The teacher tells his students to read the novel over and over again until they it.A. un

问题补充：

The teacher tells his students to read the novel over and over again until they it.

A. understand

B. understood

C. have understood

D. have been understood

答案：

(答案→)A. understand

B. understood

C. have understood

D. have been understood

解析：在时间状语从句中一般用现在时态表示将来。