Question

A man escaped from the prison last night. It was a long time ________ the guards discovered what had happened.

1. A.
   before
2. B.
   until
3. C.
   since
4. D.
   when

Answer 1

C
解析：
本題要突破定向思維，不是It was a long time before句型，注意空格后面的時態是過去完成時，前面是過去時，因此從時間概念上看應該是since．