the old man finds it useful to exercise every morning.为什么后面的从句不用it is用it呢?还有什么情况下也这样用?

the old man finds it useful to exercise every morning.为什么后面的从句不用it is用it呢?还有什么情况下也这样用? He finds a young man by the 英语阅读选择It's Sunday.There're many people in the bus.And an old man is looking here and there (到处).He wants to find an empty seat.Then he finds one.He goes to it.A small bag is on the seat.And a young man is sitting beside it.Is this se I find it hard _____ (talk) with the old man. the old man born! The old man looks ( )is the old man? ( )is the old man? Who Will Put The Bell On The Cat?　　There lives an old man in the house.In the house,there are many mice.The old man is tired of them.The old man finds a cat.Every day the cat catches the mice and eats them.　　The man is very happy.But the mice The old man seemed to be sad.=It seemed ( ) the old ( ) sad. 1).The old man who used to live in Shanghai finds the city_____.A.completely changing B.completely changed C.having been completely changed D.having completely changed 2).From the dates___on the gold coin,we decided that it was made 500 years ago.A.m ()Could you carry__for the old man A.it B.its()Could you carry__for the old man A.it B.its C.it's D.them这题选什么? the boys on the donkey and the old man climbs into it It was repairing the old clock that the old man spent the whole morning at home.为什么用REPARING The old man __his glasses Who is the old man? The old man[ ][ ][ ]his son The old man has poor____.