Sorry to say it will be years we really have classes here with only 25 students.A. sinceB

问题补充：

Sorry to say it will be years we really have classes here with only 25 students.

A. since

B. that

C. when

D. before

答案：

A. since

B. that

C. when

(答案→)D. before

解析：句意：遗憾地说在过几年之后，我们真地仅仅有25个学生。这里是固定句型it is+时间段+ before过了多长时间就……。故选D。