Last night before the exam I went over the lessonsI couldn’t keep my eyes open to stay

问题补充：

Last night, before the exam, I went over the lessonsI couldn’t keep my eyes open to stay awake any longer.

A. before

B. until

C. unless

D. when

答案：

A. before

B. until

C. unless

D. when

解析：选B。考查状语从句。句意: 昨天晚上, 考试前, 我复习功课直到我再也难以支撑的时候。until直到……的时候; before在……之前; unless除非; when当……的时候。