Computers can injure 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 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 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 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 (肘部） at the same height as the keyboard. 3) Stop something 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 should sit with your back straight. The top part of the screen should all be in front of your eyes. Your forearms（前臂）, wrists, hands and the upper（上部） part of your legs 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 necks.

　 Enjoy your computer, but use it safely.

1.A computer screen may injure your eyes if __________.

A．you sit 60 centimeters away

B．you remember to look away

C．your eyes are too close to it

D．the window is on your left or your right

2.Hand and wrist injuries are caused when you _________.

A．get plenty of exercise

B．move in the same way again and again

C．rest your wrists on something

D．keep your elbows as high as the keyboard

3.Your eyes and hands will be safe if __________.

A．you work near a window

B．you often take a rest from working

C．you use a keyboard for a long time

D．the window is behind you

4.It is good for your back and neck if you sit __________.

A．in the right way

B．for many hours

C．with the screen below your eyes

D．with your back leaning forward

5.What would be the best title for the passage?

A．How to protect your eyes

B．How to protect your hands and wrists

C．How to use a computer safely

D．How to protect your back

If you look at the sky one night and see something moving and shining that you have never seen before, it might be a comet (彗星).

　　A comet sometimes looks like a star. Like a planet, a comet has no light of its own. It shines from the sunlight it reflects (反射). Like the earth, a comet goes round the sun, but on a much longer path (轨道) than the earth travels.

       If a comet isn’t a star, what is it then?

　   Some scientists think that a large part of a comet is water frozen into pieces of ice and mixed with iron and rock dust and perhaps a few big pieces of rock. When sunshine melts (融化) the ice in the comet, great clouds of gas go trailing after it. These clouds, together with the dust, form a long tail.Many people perhaps have seen a comet. However no one knows how many comets there are. There may be millions of comets, but only a few come close enough for us to see.

　　An Englishman named Edmund Halley, who lived from 1656 to 1742, found out a lot about the paths that comets take through the sky. Some comets move out of our sight and never come back. Others keep coming back at regular times. A big comet that keeps coming back was named after Halley because he was the one who worked out when it would come back again. Maybe you have ever seen Halley’s Comets because the last time it came close to the sun and the earth was in the year 1986. Then people all over the world were outside at night to look at it. You will probably be able to see Halley’s Comets when it comes near the earth again.

1.A comet is like ________.

A. sun      B. moon     C. sunlight    D. the earth

2.A large part of a comet is ______.

A. water and rock

B. water frozen into pieces of ice and mixed with iron

C. ice, iron and rock dust

D. only a few big pieces of rock

3.Maybe many people _______.

A. haven’t seen any comets      B. have seen all comets

C. have seen a comet at daytime  D. have seen a comet

4.Some comets keep coming back ________.

A. at any time  B. at noon  C. at regular times  D. at daytime

5.Halley’s Comets came back _____.

A. in 1990    B. in 1980     C. in 1986      D. in 1989

She is planning on hiking. Let’s help her 　　　 some good ideas.