One way for students to prevent H7N9 flu virus is to openthe windows of the classroom to allow the air to ________

______important advice my teacher has given me!

erance is a kind of quality, and that is ______ it takes to do everything well.

In order to ______ a good knowledge of English, he gave up his job and went to study in an English training center.

It was Sunday and there were so many people in the streets that he found it difficult to _____ to the post office.