A、Doing potential harm to human bodies. B、Increasing moist in the users’ eyes. C、Reducing the working hours to three hours a day

Nowadays more and more people have to spend lengthy hours before computers. Computers are almost indispensable to modern life. No one can imagine the results if the computer he uses daily would break down. But computers also cause some problems. Among them is the potential harm to human bodies, especially to eyes.
    Working long hours at a computer can cause eyestrain. Recently a letter to the New England Journal of Medicine provides one explanation for the problem. Japanese researchers studied some 50 office workers who spent an average of three hours a day at a terminal. Since blinking keeps eyes moist—thus reducing strain—the researchers counted blinking rates under different conditions. The workers averaged 22 blinks a minute when relaxed, ten blinks a minute while reading a book and just seven a minute while reading text on a computer screen. Thus people keep the least moisture in their eyes when they are working at a computer and feel more strained. Furthermore, the computer workers also kept their eyes open wider, which meant moisture evaporated more quickly.     If you work at a computer screen, close your eyes periodically. That spreads a tear film and rests your eyes. And remember to blink more often. In this way you can reduce the side effect caused by using computer to a greater extent.
16. What is the result of using computer in our daily life?
17. What is the cause of eyestrain?
18. What are those who spend long hours before computers supposed to do?