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：
本题要突破定向思维，不是It was a long time before句型，注意空格后面的时态是过去完成时，前面是过去时，因此从时间概念上看应该是since．