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  3. A new kind of radar has been developed for space-age travelers. A working laboratory model of a new system of radar that makes u

A new kind of radar has been developed for space-age travelers. A working laboratory model of a new system of radar that makes u

admin2015-12-31  28
问题     A new kind of radar has been developed for space-age travelers. A working laboratory model of a new system of radar that makes use of a beam of light is said to be ten thousand times more accurate than the best comparable system of radar that uses microwaves.
    The model has shown that this radar system (known as laser-doppler radar) can measure with absolute precision speeds varying from spaceship orbital injection velocities (速度) of five miles per second down to virtual stops—speeds of less than one ten thousandth of an inch per second. According to the scientists who are developing this system, such fine measures of velocity are of prime importance in space missions. In a rendezvous (会合, 会合点) between two spaceships, or in a landing approach by a vehicle onto an orbiting space station, a bump could rip open a ship’s skin, or a nudge (轻触) could knock the station out of its orbit.
    The light-beam radar, which operates at a frequency of trillions of cycles per second, could easily detect and measure the movement of a vehicle edging up to a satellite space station even at a small fraction of an inch per second. A control system using so precise a signal as this would allow a huge vehicle to dock at a space station as lightly as a feather.
Which of the following statements is implied but not stated?
选项 A、Microwave radar operates at a higher frequency than laser-doppler radar.
B、Laser-doppler radar is more accurate than microwave radar.
C、The light-beam radar can measure only slow speeds with absolute accuracy.
D、Microwave radar does not insure absolute precision in measuring varying speeds.
答案D
解析 本题可通过排除法找到答案。从文中第一段第二句和第二段第一句可知，激光多普勒雷达系统比使用的微波雷达系统精确万倍，因此选项B在文中已提出，故可排除；同时根据文中第一段第二句可知，这种新型雷达系统尚在试验中，而已经使用的是微波雷达系统，因此选项A可排除；文中第二段第一句指出，这种激光雷达系统能够绝对精确地测量速度变量，因此选项C可排除。本题亦可通过综合推理法找到答案。文中在第一段第二句提到多普勒雷达系统比已经使用的微波雷达系统精确万倍，而在第二段中又举例说多普勒雷达能绝对精确地测量不同的速度。综合上述信息，我们可以推断出采用微波技术的雷达系统不能确保各种速度的精确测量。因而选项D正确。
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