the rain falling so frequently ,it becomes more and more difficult to carry on

问题描述:

the rain falling so frequently ,it becomes more and more difficult to carry on
_______ the rain falling so frequently ,it becomes more and more difficult to carry on the rescue work.
A.since B.with C.as D.for\
应该选B.为什么不是A?众所周知的原因“由于雨下的很频繁,营救工作很难进行”

since 引导一个句子,如果用since 应该为 since the rain is falling so frequently