The bhagirathi and the Alaknanda merge at Deoprayag to form the Ganga with their speeds in the ratio `1 :1.5`. The cross-sectional areas of the Bhagirathi, the Alaknanda and the Ganga are in the ratio `1 : 2 :3`. Assuming stremline flow, the ratio of the speed of Ganga to that of the Alaknands is
A. `7:9`
B. `4:3`
C. `8:9`
D. `5:3`