英语语法中,I think it difficult to do my work.怎么理解it 为什么不加is?

I think it difficult to answer this question 为什么可以it 不加is? 什么时候用it什么时候用it is,如I think it difficult to do my homework. I think it is difficult to do the work in an hour.句子正确吗? 为什么有的时候是I think 有的时候是I think it is difficult to do sth 简单的英语语法提问!I think,is difficult to learn it,but I decide to l I think it hard to fall asleep in night.请问it后为什么不加is. I think it difficult to learn English well句中为什么用it? I find that it is difficult to do the work .句子正确吗? I think it difficult中间能加IS吗 ① I think it my duty to do sth.和 i think it IS my duty to do 用to ,it,do,think,well,is,anything,I,difficult.造句 形式主语it 难题Do you think it difficult to work out this question