单项选择题

Laser-doppler radar is especially valuable in space missions because ()

A. it can measure the movement of a spaceship less accurately than a microwave radar
B. it is a new system of radar
C. it provides precise measures of the velocity of space vehicles
D. it is one thousand times more precise than microwave radar

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单项选择题

Implied but not stated is that()

A. laser-doppler radar is more accurate than microwave radar
B. microwave radar operates at a higher frequency than laser-doppler radar
C. the light-beam radar can measure only slow speeds with accuracy
D. microwave radar may not ensure absolute precision in measuring varying speeds

单项选择题

21()

A. under the thumb
B. below the hands
C. subject to the palm
D. in the fingers