39. When a driver is traveling at a speed of v1, they hear the frequency of a distant whistle as f₁. When they reduce their speed to v2, the frequency of the whistle is heard as f2. The car is moving toward the sound source. Assuming the sound source is stationary relative to the ground, what is the speed of sound?
(A)
(B)
(C)
(D)
(E)
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統計: A(2), B(0), C(0), D(1), E(0) #3421234
統計: A(2), B(0), C(0), D(1), E(0) #3421234