根据短文内容，从下列七个选项中选出能填入空白处的最佳选项。
Sleep plays an important role in brain (大脑) development. Children should get enough sleep.
A study says that because of being short of sleep, it is much harder for children to do something carefully. And also they become forgetful and easy to make mistakes. Another study shows that the right amount of night—time sleep is just as important for children's development as healthy eating and taking exercise.
In general a younger child needs more sleep than an older one. Children at the age of 5-11 will need 10-12 hours of sleep a night while children at the age of more than 11 will need less hours.
In fact, many parents don't know how to help their children get enough sleep. Here is something you can do. For children at the age of 5-11, a 30-40 minutes' routine (常规) before sleep is helpful. In the activities, children relax and enjoy themselves a lot, and they will go to sleep more easily.
Children at the age of more than II may go to bed late in the evening, talking with friends online, playing games or watching TV. And even they will be tired during the day. So limit(限制) your children's use of the Internet, games and the TV before they go to bed.
A. If not, many problems will come to them.
B. Why does a child need so much sleep?
C. How many hours of sleep is enough for a child?
D. So they will find it, difficult to get up in the next morning.
E. It includes a bath, reading a story together and so on.
F. Taking exercise is as important as enough sleep for children.
G. And don't allow them to have a computer or TV set in their bedroom.