Computers can injure(伤害)you. Most other injuries happen suddenly．For example，if you fall off a bike and break your arms, it happens very quickly. But computer injuries happen slowly． You probably know how to ride a bike safely. Now learn to use a computer safely．  Your eyes Too much light can injure your eyes, so never sit too close to a computer screen. Your eyes should be more than 50 centimeters from the screen. Don’t forget 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 on(反射)the screen. If the window is in front of you，the sun and the screen will both shine into your eyes． Your hands and wrists(手腕) Hand and wrist 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(肘)as high 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 the wrong way, you can injure your back or your neck. So you shouldn’t bend your back when you sit. The top part of the screen should be in front of your eyes. Your forearms, wrists, hands and the upper part of your legs should all be parallel(平行)to the floor. If you are sitting for a long time, get up every half an hour and exercise your arms, legs and neck． Enjoy your computer, but use it safely．
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