①
宾语从句+宾语补足语的结构为了保持句子平衡,常用it作形式宾语,把真正的宾语从句置于句末,常见的it作形式宾语的
谓语动词有believe,find,make,guess,suppose等。
He didn't make it clear when and where the meeting would be held.
②某些
及物动词或短语不能直接加宾语从句,此时用it作形式宾语,然后再接宾语从句,此种用法常见于like,dislike,hate,appreciate等。
I'd appreciate it if you would like to teach me how to use the computer.