Teachers always tell us to try to be _______ honest student today and _______ useful man tomorrow．（　　）

﹣﹣George，how can you prove（证明）the earth is round？

﹣﹣I can't，sir．_______，I never said it was．（　　）

I hope everyone can care about ______ the environment and stop ______ things．（　　）

﹣I want to borrow the book，but I don't know how long it may ______．

﹣For two weeks．（　　）

Do you want to be healthy？______．Smiling can help you stay healthy．（　　）