请教 885， section 4 No.20

以下是引用clevercat在2004-3-9 1:04:00的发言：
20.When rates were raised in 1985,postal service officials predicted they would make further rates increases unnecessary for at least three years.



A, they would make futther 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


E,further rate increases will not be needed


正确答案是D，可我怎么也看不出C错在哪里，it 在这里作形式主语呀。