请教，885 sec.04, 20题

20.   When rates were raised in 1985, postal service officials predicted they would make further rate increases unnecessary for at least three years.

(A) they would make further rate increases unnecessary

(B) they would mean that further rate increases would not be needed

(C) that it would not be necessary for further rate increases

(D) that the increase would make further rate increases unnecessary（D）

(E) further rate increases will not be needed

答案是D,为什么C不对?

C中的it没有可以指代的对象

it可以指代that从句 it is possible that he will come

it可以指代to do结构 it is impossible to convince him.

thanks for help, then if the answer is: that it would not be necessary to further increase rate, it will be right?