下面短文中有四处（第1﹣4题）需要添加小标題．阅读短文，然后从方框中所给的A、B、C、D四个选项中选出符合各段意思的小标题，并完成第5题．

    Sleep plays an important role in our life． A lack of sleep can influence our ability to work and study．

（1）　　

    Normal people need 7 to 9 hours of sleep every night． But for teenagers， a healthy amount（数量） is about 8 to 10 hours． Sadly， only $\frac{1}{3}$ of people manage that．

（2）　　

    Tiredness usually reaches its highest twice a day， at 2 a．m． and 2 p．m． That explains whys students easily fall asleep in afternoon classes． So sleeping at noon for a while helps us work better in the rest of the day．

（3）　　

    People can make mistakes if they don't get enough sleep． Students cannot pay attention in class or do well in sports． Drivers who have fallen asleep while driving have caused 1%﹣10% of the traffic accidents in our life． And we can imagine what will happen if a doctor feels sleepy at the operating﹣table!

（4）　　

    There are several ways that can help us sleep better， such as avoiding drinks that make us excited late in the day， going to sleep at the same time each night， and sleeping in a comfortable place that is dark， quiet and warm．

A． Bad influences

B． Sleeping hours

C． The most tiring moments

D． Good sleeping habits

（5）The passage mainly encourages us to 　　． （不得超过5个单词）