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  3. There are cockroaches(蟑螂)everywhere on Earth except the places that are covered with ice. Scientists have discovered about 3 , 5

There are cockroaches(蟑螂)everywhere on Earth except the places that are covered with ice. Scientists have discovered about 3 , 5

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问题     There are cockroaches(蟑螂)everywhere on Earth except the places that are covered with ice. Scientists have discovered about 3 , 500 different species of cockroach. There is just one human species! Cockroaches can be anything in size from about five mm to nine cm. Although five mm is very small, nine cm is as long as a large rat.
    It is very difficult to catch most cockroaches. They "see" with the hairs on their bodies. These hairs can feel the smallest movement in the air, so the cockroaches know immediately something moves, and run to safety.
    Of all the species of cockroach, fortunately only three live among humans and are a serious problem. They are the German, the Oriental, and the American. One egg case of the German cockroach can produce as many as seven million cockroaches in 12 months!
    Our main problem with cockroaches is that not only do they look ugly to us, but they also carry diseases.(69)They are particularly dangerous in hospitals as they eat all kinds of hospital waste or get it on their bodies. They can then carry this waste, which may contain dangerous bacteria, on to food which is then eaten by people in the hospital.
    Most of the bacteria that cause food poisoning have been found in the stomachs of cockroaches, so it is important that cockroaches should be kept out of restaurants and other places where food is prepared.
     (70)Many people work and try to destroy cockroaches, but as soon as they find one way of doing it, the cockroaches "learn" how to deal with it. Electricity does not always kill them and they can avoid most poisons or "learn" how to deal with others. At one time, scientists thought that radiation would kill them, but they have been on Earth for about 300 million years, and it does not harm them as much as it does us.
    It seems probable that when there are no longer human beings living on the Earth, cockroaches will still be here.
Why should cockroaches be kept out of restaurants and other places where food is prepared?
选项
答案Because most of the bacteria that cause food poisoning have been found in the stomachs of cock—roaches．
解析 (根据文章倒数第三段可知。)
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