If _________, he promised that he would try his best to improve people’s living conditions [ ]

Be careful with the knife, ______ you’ll be hurt.

Plants _________carbon dioxide and at the same time _________oxygen. So we may put some in our bedrooms to purify the air.

In many countries more and more forests and even agricultural land are being lost to development, _______ much of the land to become desert.

How long do you think it will be ________ the computercompany puts forward a new product