.Your son has kept _________ for two hours. You’d better ask him to have a rest.
Do you know what__________ before you __________?
The price of the book is __________ so I would rather not buy it.
My hobby is collecting stamps.I need __________ before I have 3000 stamps.
The number of the classes in our school is __________ than__________ of any other school in Nanjing.
He was just leaving ________ the telephone rang.