Many injuries（傷害）happen suddenly.For example，if you fall off a bicycle and break your arm，it happens very quickly.But computer injuries happen slowly.
Your eyes	Too much light can injure your eyes，so never sit too close to a computer screen.Your eyes should be at least 50 centimeters from the screen.Remember to look away from it sometimes.This gives your eyes a rest.When you use a computer，the window should be on your left or your right.If it is behind you，the light will reflect（反射）on the screen.If the windows are in front of you，the sun and the screen will both shine into your eyes.
△	Hand and wrist（手腕）injuries can happen because the hands and wrists are moved in the same way hundreds of times.If you use a keyboard for a long time，follow these three rules： （1）Rest your wrists on something. （2）Keep your elbows at the same height as the keyboard. （3）Stop sometimes and exercise your hands，wrists and fingers in a different way.
Your back	Some people sit for many hours in front of a computer.If you sit in a wrong way，you can injure your back or your neck.So you should sit with your back straight.The top part of the screen should be in front of your eyes.Your forearms，wrists and hands should all be parallel（平行）to the floor.If you are sitting for a long time，get up every 30 minutes and exercise your arms，legs and neck.
Enjoy your computer，but use it safely.

（1）Which kind of injuries may happen slowly？

C

C

A．You use your computer correctly.
B．You fall off a bicycle and break your arm.
C．You sit in a wrong way for many hours in front of a computer.
（2）How far should you keep your eyes from the screen？

B

B

A．At least 30 cm.
B．At least 50 cm.
C．At least 70 cm.
（3）Which can best be for "△"？

A

A

A．Your hands and wrists.
B．Your head and neck.
C．Your legs and feet.
（4）What does the writer tell us in the passage？

B

B

A．You'd better not use the computer.
B．Enjoy your computer，but use it safely.
C．Keep away from the computer to be safe.