The poor children ______ worry about ________ money to go to school.
You’d better try different ways you can think of maths problems. It’s good for you to learn maths well.
Can you make sure ________ he will come here today, Linda?
—What should we do to prevent H7N9 bird flu? —We must from crowded places.
—It’s a long story, but you will find that there are few new words in it . —Good! it will be too hard for children.
Which is _____ difficult, this one or the other two?