单项选择题

Laser-dopple radar ______.

A．measures the movement of a spaceship by means of light beam
B．makes use of microwaves
C．makes use of sound waves
D．both A and B
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单项选择题
Laser-dopple radar is especially valuable in space missions because it ______.
A．is one thousand times more precise than microwave radar
B．provides precise measures of the velocity of space vehicles
C．is a new system of radar
D．can measure the movement of a spaceship less accurately than a microwave radar
单项选择题
Implied but not stated ______.
A．Laser-dopple 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-dopple radar
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