如果是一个简单的wh+型名词从句,且补足语是一个形容词/名词这样的结构的话,不改用it,因为it是代表事件的,你放进去后就没有意义了。但是如果是不定式作补足语,那问题来了,如:
以下为自编的句子,不权威,只是说明原理
1. I find it very difficult to wash away what you wrote on the shirt you bought at the local market.
2. I find what you wrote on the shirt you bought at the local market very difficult to wash away.
此时要用it了,因为宾语太长了。读第2句时你晕不晕。