有两个句型一直不明白,关于it 和it is

题目

有两个句型一直不明白,关于it 和it is
有两个句型一直不明白：
1.He found it difficult to climb the stairs.
2.He thinks that it is better to see the movie than to read the book in original.
为什么第一个是it而第二个是it is?

答案

前者是it作形式宾语,后者是it is作宾语从句中的主语和系动词两者有区别,但也可以互换,请看：He found it difficult to climb the stairs.=【He found that it is difficult to climb the stairs.】He thinks that it...