Two equal masses `m_1` and `m_2` moving along the same straight line with velocites `+3 m//s` and `- 5 m//s` respectively collide elastically. Their velocities after the collision will be respectively.
A. `+4m//s` for both
B. `-3m//s" and "+5m//s`
C. `-4m//s "and" +4m//s`
D. `-5m//s" and "+3m//s`