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.
.
A. `v_1gtv_2ltv_3`
B. `v_1=v_2gtv_3`
C. `v_2gtv_3gtv_1`
D. `v_1gtv_3gtv_2`