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
网友回答
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5-10年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。