What do you call this in English?—It’s a stamp. It is used ______ sending. [ ]

I thought there would be many students in the hall, but when I got in, I found ______.

The young mother often _________ her child alone at home.

It is said that ____ young people may lose the abilities to hear after five years if they listen to MP4 players which are too loud for more than five hours a week.

_______ is the drink, please?—Ten yuan a tin.[ ]