Plants _________carbon dioxide and at the same time _________oxygen. So we may put some in our bedrooms to purify the air.
Is it in the factory__ you visited last week__this kind of car is made﹖
---David has made great progress recently. ---_____, and______ .
Who did the teacher have ___ an article for the wall newspaper just now?
Great changes have taken place in that school. It is no longerit was 20 years ago, it was so poorly equipped.
His pale face suggested that he ______ ill and the teacher suggested that he _______ the doctor.