I think it difficult中间能加IS吗

I think it difficult中间能加IS吗 I think it difficult to answer this question 为什么可以it 不加is? I think math is difficult,I need (h)with it. I think geography is difficult to learn it. I think it is difficult to do the work in an hour.句子正确吗? difficult,i,chinese,think,is 为什么有的时候是I think 有的时候是I think it is difficult to do sth 什么时候用it什么时候用it is,如I think it difficult to do my homework. i think chemistry is very difficult,but Vince thinks it is v I think maths is very difficult,but I’m not b______ in it. 简单的英语语法提问!I think,is difficult to learn it,but I decide to l I think math is very difficult.同义词