sb. think/find + it + adj. + to do sth.中的 it 后面可不可以加 is 啊?比如:I found it hard to answer the question. 有没有 I found it is hard to answer the question. I think it impossible for a boy of 9 to finish this task. 有没有 I think it is impossible for a boy of 9 to finish this task.