______ came that Prime Minister David Cameron(卡梅伦首相) blamed the worst riots(骚乱)in Britain the other day.
Wait till you are more_____. It’s better to be sure than sorry.
In the future people can read books only _____ computers, not _____ paper.[ ]
Tom is a good boy and he writes _________ in his class.
We can’t live _____ air or water.[ ]