Given below are two statements: one is labelled as Assertion $A$ and the other is labelled as Reason $R$.
Assertion $A$: Body $P$ having mass $M$ moving with speed $u$ has a head-on elastic collision with another body $Q$ having mass $m$ initially at rest. If $m << M$,body $Q$ will have a maximum speed equal to $2u$ after the collision.
Reason $R$: During an elastic collision,the momentum and kinetic energy are both conserved.
In the light of the above statements,choose the most appropriate answer from the options given below:

• A
  $A$ is not correct but $R$ is correct.
• B
  Both $A$ and $R$ are correct but $R$ is $NOT$ the correct explanation of $A$.
• C
  Both $A$ and $R$ are correct and $R$ is the correct explanation of $A$.
• D
  $A$ is correct but $R$ is not correct.