10. When the observer and the sound source are stationary relative to each other, the observed frequency is f. Suppose the observer and the source are moving toward each other. If the observer's speed is 0.25v and the source's speed is also 0.25v, where v is the sound speed. What will be the observed frequency?
(A) 5f/4
(B) 3f/4
(C) 4f/3
(D) 3f/5
(E) 5f/3
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統計: A(0), B(0), C(0), D(0), E(2) #3421205
統計: A(0), B(0), C(0), D(0), E(2) #3421205