Two identical balls `A and B` having velocity of `0.5 m//s and -0.3 m//s` respectively collide elastically in one dimension. The velocities of `B and A` after the collision respectively will be
A. `+0.5m//s " and " +0.3m//s`
B. `-0.3m//s " and " +0.5m//s`
C. `+0.3m//s " and " 0.5m//s`
D. `-0.5m//s " and " +0.3m//s`