The discovery of gold in Australia led thousands to believe that a fortune ______.

A. had been making  B. was making  C. was to be made D. would make

这道题目选择C，不明白为什么要有一个被动在里面，那B选项改成 was being made 是不是也可以选，我选择的是D，都是表示将来，难道却别就是因为要一个被动吗？