There aren’t any___ between them.

-You look so worried, what’s wrong?  -More and more people like me begin to worry about the ______ pollution after the haze (雾霾) appeared in Beijing and some other cities in China. 

Mr. Wu is a teacher with _______. He often tells us some of his unusual _______ in America.

—What does your mother do?—She is ___. 

There are three __in the office.