$A$ body of mass $m$ moving with velocity $v$ collides with another body of mass $nm$ moving in the same direction with velocity $kv$. If the first body comes to rest after the collision,what is the velocity of the second body?

• A
  $\frac{nv}{1 + nk}$
• B
  $\frac{nv}{1 - nk}$
• C
  $\frac{(1 - nk)v}{n}$
• D
  $\frac{(1 + nk)v}{n}$