A small source of sound moves on a circle as shown in figure and an observer is sitting at O. Let `v_1,v_2,v_3` be the frequencies heard when the source is at A,B and C respectively.

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A. `n_(1)gtn_(2)gtn_(3)`
B. `n_(2)gtn_(3)gtn_(1)`
C. `n_(1)=n_(2)gtn_(3)`
D. `n_(2)gtn_(1)gtn_(3)`