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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 one special point of lasers?
选项 A、It’ s possible to store the light beam.
B、The gases are heated and cooled.
C、There are some different types of lasers.
D、They can use the beam in a continuous stream.
答案A
解析 根据第二段第四句“One special point of lasers is that the light，beam can be stored．”可知，激光的特别之处在于它的光束可以被存储。故选A。
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