If you want people to treat you nicely, you have to treat        nicely, too.

Mr. Green didn’t post the letter _________. He asked his son to do it for him. 

—How about the pollution in the countryside?—Luckily, it's not as serious as _______ in the big cities.

 —Who’s your best friend? Is ____ a boy or a girl?—A boy. I often play with _____ after school.

Miss Fang is ________ English teacher. ________ is a good teacher.