the students there had to believe what the teacher told them bacause the had no other sources of information _____

问题描述:

the students there had to believe what the teacher told them bacause the had no other sources of information _____
A.otherwise B.so C.however D.besides
请问为什么,还有,把句子翻译一下.

A.otherwise 否则
学生们不得不相信他们的老师告诉他们的东西,否则,他们没有其他的信息来源