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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

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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.
This selection could be entitled______.
选项 A、The Function of Radar
B、Problems in Space Navigation
C、Radar for the Space Age
D、Space Stations
答案C
解析 文中第一句是主题句，也是解答这道要旨题的依据。主题句说：“一种新的雷达已经为太空时代的旅行者开发出来了。”文中的其他句子都是围绕这个主题句而展开的。故选项C与主题句的含义相符合。
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