I often write ________ letter to my pen friend.

. ---- You like to surf the Internet. Do you know the meaning of “WWW”?---- Of course. It means _______.

__________ mother is a middle school teacher．

-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. 

Look! There are some______ on the table.