Our body grows most while we are asleep. The _____ children usually need more sleep. After we have plenty of rest, we can do our lessons better. Boys and girls about fifteen need nine hours of sleep. If we don't get enough _____ air, we will feel tired when we wake up. While in bed, we mustn't _____ our head. Our lungs need to get enough air, so we'd better open our window _______ and let fresh air in. Scientists say that cool air is better than _____ and sleeping in heated rooms does no good to our health.

We work eight-and-a-half to nine hours a day. We survival activities -- these are things like eating and bathing and looking after kids -- about three hours a day.

中国大学MOOC: We shall not need such a big house ______ the children all left home.

After placing an order, we will need to sign the and make legal of all the details.

中国大学MOOC: Many banks work with so many different customers and accounts that they need _____ to record all transactions.