Read the article. Match the title to each paragraph.

(Đọc bài văn. Nối tiêu đề đúng với mỗi đoạn văn)

a. A twenty-first century problem

b. The problem of light and screens

c. Why do we need to sleep?

1. Why do we steep? One thing we do know is that it's good for our physical and mental health Physically, sleep helps prevent sickness and keeps our body healthy. Mentally, we study and work better when we sleep for about eight hours the previous night.

In this country lack of sleep is becoming a big problem. The average American sleeps less than seven hours a night-that's two hours loss than a century ago. Our modern 24-hour-day lifestyle means that more and more of us are working at different times of the day-and night. We often stay up late into the night, and some of us even work all night and sloop during the day. This is a problem because our body's natural clock is connected with the movement of the sun. If we don't sleep at night for long periods, it can be bad for our health.

But perhaps the biggest problem comes from electric lights and screens. Modern cities use bright LED lights through the night, which changes the way we sleep. In addition, the screens of our computers, tablets, and smartphones all send out blue light. The bluer and brighter the light, the more difficult it is to get tired and go to sleep. As a result, some medical experts suggest that we shouldn't watch more than two hours of television per day, and that we should stop looking at screens (including phones) one hour before we go to bed But how many of us will take this advice?