Two masses `m_(A)` and `m_(B)` moving with velocities `v_(A)` and `v_(B)` in opposite direction collide elastically after that the masses `m_(A)` and `m_(B)` move with velocity `v_(B)` and `v_(A)` respectively. The ratio `(m_(A)//m_(B))` is
A. 1
B. `(v_(A)-v_(B))/(v_(A)+v_(B))`
C. `(m_(A)+m_(B))//m_(A)`
D. `v_(A)//v_(B)`
