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  3. A very interesting and important development in science is a device called laser. A laser is a machine which produces a light be

A very interesting and important development in science is a device called laser. A laser is a machine which produces a light be

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问题    A very interesting and important development in science is a device called laser. A laser is a machine which produces a light beam. The light produced by a laser is a very special kind of light. The light, called a laser beam, is powerful and can be made to do many things. The laser was first developed in 1960, about more than half a century ago.
   There are many different uses for lasers and several different types have been developed. Some use gases to produce the light beam. The gases are heated and cooled, and these processes cause the gases to produce energy in the form of light. One special point of lasers is that the light beam can be stored. If the stored light is then suddenly let go, it is extremely powerful. The light from a laser beam can be used either by storing it and letting it go suddenly, or by using it in a continuous stream.
   There are three important areas where the control of the laser beam has been put into use by scientists. These areas are industry, communications, and medicine. In each area, the scientists have been able to use the laser to do things that they could not do in another way. The laser has been very helpful.
   In industry, the laser beam has been used for measurement and drilling. When something large is being built—for example, a large bridge—it is important to have very accurate measurements. By accurate measurement, lasers are also helpful in laying down pipelines over long distances. As lasers become more common in industry, there will be more and more uses for them.
What is important in building large things?
选项 A、To drill holes accurately.
B、To lay down long pipelines.
C、To cut pipes by lasers.
D、To measure accurately.
答案D
解析 根据最后一段第二句“When something large is being built—for example，a large bridge—it is important to have very accurate measurements．”可知，在建造大型建筑物时，精确的测量很重要。故选D。
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