Given below are two statements: one is labelled as Assertion $(A)$ and the other is labelled as Reason $(R).$
Assertion $(A):$ Kinetic energy of a system can increase without applying external force on the system.
Reason $(R):$ If external forces are absent,then the work done by internal forces is equal to the change in kinetic energy.
In the light of the above statements,choose the most appropriate answer from the options given below:

• A
  Both $(A)$ and $(R)$ are true and $(R)$ is the correct explanation of $(A).$
• B
  Both $(A)$ and $(R)$ are true but $(R)$ is $\text{NOT}$ the correct explanation of $(A).$
• C
  $(A)$ is true but $(R)$ is false.
• D
  $(A)$ is false but $(R)$ is true.