English is used ____ a second language ___ people in many countries.

问题描述:

English is used ____ a second language ___ people in many countries.
A.as;for
B.for;by
C.as;by
D.by;for
我知道答案是C,请问为什么不是A呢?我觉得应该是as;for,请赐教.

C
被人使用,就用by