题干

       Taking away a city's rubbish is a big job. Every day trucks come into a city to collect it. Most rubbish is made up of things we can't eat or use. If we kept these things we would soon have a mountain of rubbish.
       In some cities the rubbish is collected and taken outside of the city to a dump(垃圾站). Often the city dump is placed where the ground is low or there is a big hole. The kitchen rubbish is broken into small pieces and sent into the sewage system. The sewage system takes away the used water from toilets, bathtubs(澡盆) and other places.
        To keep mice and flies away, some earth is used to cover the newly dumped rubbish. Later, grass may be planted on the rubbish-filled land. Finally, a house or a school may be built there, and then you’d never know that this had once been an old rubbish dump.
       In other cities the rubbish is burnt in special places. The fire burns everything but the metal. Sometimes the metal can be used again in factories where things are made of metal. The food parts of rubbish are put in special piles where they slowly change into something called humus(腐殖土), which looks like black earth. It is rich with kinds of things that feed plants and help make them grow.
上一题 下一题 0.0难度 选择题 更新时间:2020-01-19 05:45:59

答案(点此获取答案解析)

同类题3

阅读理解

    Far from the land of Antarctica (南极洲), a huge shelf of ice meets the ocean. At the underside of the shelf there lives a small fish, the Antarctic cod.

    For forty years scientists have been curious about that fish. How does it live where most fish would freeze to death? It must have some secret. The Antarctic is not a comfortable place to work and research has been slow. Now it seems we have an answer.

    Research was begun by cutting holes in the ice and catching the fish. Scientists studied the fish's blood and measured its freezing point.

The fish were taken from seawater that had a temperature of -1.88°C and many tiny pieces of ice floating in it. The blood of the fish did not begin to freeze until its temperature was lowered to

    -2.05°C. That small difference is enough for the fish to live at the freezing temperature of the ice-salt mixture.

    The scientists' next research job was clear: Find out what in the fish's blood kept it from freezing. Their search led to some really strange thing made up of a protein (蛋白质) never before seen in the blood of a fish. When it was removed, the blood froze at seawater temperature. When it was put back, the blood again had its antifreeze quality and a lowered freezing point.

    Study showed that it is an unusual kind of protein. It has many small sugar molecules(分子)held in special positions within each big protein molecule. Because of its sugar content, it is called a glycoprotein. So it has come to be called the antifreeze fish glycoprotein, or AFGP.