8. A sound source of frequency f moves at a velocity of \( v_s \), while a detector moves at \( v_d \) in parallel. If the speed of the sound in air is v, what is the frequency of the sound as measured by the detector?
(A)\( \frac{v+v_d}{v+v_s}f \)
(B)\( \frac{v-v_d}{v-v_s}f \)
(C)\( \frac{v+v_s}{v+v_d}f \)
(D)\( \frac{v-v_d}{v+v_s}f \)

(E)\( \frac{v+v_s}{v-v_d}f \)

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