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【单选题】
Bats navigate and search out prey by emitting, and then detecting reflection of, ultrasonic waves, which are sound waves with frequencies greater than can be heard by a human. Suppose a bat emits ultrasound at frequency f be = 82.52kHz while flying with velocity v b = 9.00m/s as it chases a moth (蛾) that flies with velocity v m = 8.00m/s. What frequency f md does the moth detect? What frequency f bd does the bat detect in the returning echo from the moth?A.
f md = 82.8kHz, f bd = 83.0Hz
B.
f md = 82.8Hz, f bd = 83.0kHz
C.
f md = 82.8kHz, f bd = 83.0kHz
D.
f md = 82.8Hz, f bd = 83.0Hz
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