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  3. Thousands of years ago man used handy rocks for his surgical operations. Later he used sharp bones or horns, metal knives and mo

Thousands of years ago man used handy rocks for his surgical operations. Later he used sharp bones or horns, metal knives and mo

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问题    Thousands of years ago man used handy rocks for his surgical operations. Later he used sharp bones or horns, metal knives and more recently, rubber and plastic and that was where we were stuck, in terms of surgical instruments, for many years. In the 1960s a new tool was developed, one which was, first of all, to be of great practical use to the armed forces and industry, but which was also, in time, to change greatly the art and science of surgery.
   The tool is the laser(激光) and it is being used by more and more surgeons all over the world. As we all know, light is hot: any source of light—from the sun itself down to a simple match burning—will give warmth. But light is usually spread out over a wide area. The light in a laser beam(激光束) , however, is concentrated(集中的). This means that a light with no more power than that produced by an ordinary electric light bulb becomes intensely strong as it is concentrated to a pinpoint-sized (针尖大小的) beam.
   Experiments with these pinpoint beams showed researchers that different energy sources produce beams that have a particular effect on certain living cells. It is now possible for eye surgeons to operate on the back of the human eye without harming the front of the eye, simply by passing a laser beam right through the eyeball. No knives, no stitches (缝针), no unwanted damage—a true surgical wonder. Operations which once made patients tired and in need of a long period of recovery time now leave them feeling calm and comfortable. So much more difficult operations can now be tried.
   The rapid development of laser techniques in the past ten years has made it clear that the future is likely to be very exciting. Perhaps some cancers will be treated with the laser in a way that makes surgery not only safer but also more effective. Altogether, tomorrow may see more and more information coming to light on the diseases which can be treated medically.
The laser beam is very strong because______.
选项 A、it is artificially lighted
B、it gives off heat in all directions
C、it contains a concentrated beam of the light
D、its temperature increases due to the heat of the sun
答案C
解析 根据第二段最后两句可知，激光束有强大的威力是因为其光束非常集中，所以C项符合题意。
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