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.

下列关于导盲犬主要特征和行为的叙述，正确的是（    ）

①体温恒定   ②变温动物  ③胎生动物  ④体表被毛  ⑤具有社会行为  ⑥靠四肢行走  ⑦导盲犬的导盲行为属于先天性行为．

    Volunteers are people who do a job for the satisfaction (满足感)of helping others．

    Volunteers do many different types of jobs．Some volunteers read books onto tapes so that people with poor eyesight（视力）can listen．

    Some volunteers deliver meals to elderly or sick people.

    Some volunteers help tourists (游客) who visit a city during a major event like the Olympic Games or the Commonwealth Games.

    Volunteers help whenever a community is hit by a natural（自然的）disaster（灾害）.

    Volunteers assist（援助，帮助）in putting out（扑灭）bush（灌木丛）fires．They might also help to evacuate（疏散）people from areas that have been flooded or hit by an earthquake（地震）or tsunami（海啸）.

    A community may not recover（恢复正常）without the help of volunteers.

    Some communities require volunteers more than others.

    Communities that don't have much money require a great deal of help from volunteers.

    Communities with a large number of elderly people might require more help from volunteers than communities with more young people．Without volunteers, some communities couldn't operate.