题目内容
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Laser-doppler radar is especially valuable in space missions because ______. ()
A．it is one thousand times more precise than microwave radar
B．it provides precise measures of the velocity of space vehicles
C．it is a new system of radar
D．it can measure the movement of a spaceship less accurately than a microwave radar
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更多“Laser-doppler radar is especia…”相关的问题
Implied but not stated is that ______. ()
A．laser-doppler radar is more accurate than microwave radar
B．microwave radar may not ensure absolute precision in measuring varying speeds
C．the light-beam radar can measure only slow speeds with accuracy
D．microwave radar operates at a higher frequency than laser-doppler radar
The model has shown that this radar system, known as laser-doppler radar, can measure with absolute precision speeds varying from spaceship orbital injection (进入) 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 (对接) 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 could knock the station out of its orbit.
The light-beam radar, which operates at a frequency of trillions (百万兆) of cycles per second, could easily detect and measure the movement of a vehicle edging up to a satellite space station. 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.
Laser-doppler radar ______. ()
A．measures the movements of a spaceship by means of light beam
B．makes use of microwaves
C．makes use of sound waves
D．Both A and B
Which of the following statements is not true according to the passage ______. ()
A．accuracy ill speed measurement is essential to spaceships
B．the speeds of space vehicles will vary
C．inaccuracies in measurement could cause accidents in space missions
D．a bump could affect the preciseness of the laser-doppler radar
The author of this passage probably intended to explain ,______.
A．exactly how radar works
B．why the British used radio waves in their device
C．how radar(word and device)came to be
D．how radar helped the British win the Battle of Britain
Besides being of critical importance to pilot，radar is (20)______ for air traffic control，for tracking ships at sea，and for tracking weather systems and storms.
(11)
A．through
B．for
C．on
D．against.
Radar enabled the English to______.
A．detect German planes on their way to London
B．direct the outnumbered RAF planes effectively
C．confuse German bomber pilots
D．both A and B
By moving the radar beam around slowly in circles, we can ______ the surroundings.
A．explore
B．expose
C．exploit
D．expand
An appropriate title for this passage would be ______. ()
A．Rendezvous in Space
B．Landing at a Space Station
C．New Radar for the Space Age
D．Space Navigation
