It may be 5 or 10 years it is possible for people to find a space station on the moon.A.

问题补充：

It may be 5 or 10 years it is possible for people to find a space station on the moon.

A. since

B. before

C. after

D. when

答案：

A. since

(答案→)B. before

C. after

D. when

解析：考查连词和句型：A. since自从，B. before在…前面，C. after在…后面，D. when当…时候，句意：可能还要5-人们才能发现月球上有个太空站。使用了句型：It may be+一段时间+before….“要…长时间才能够”，选B。