Given below are two statements: one is labelled as Assertion $(A)$ and the other is labelled as Reason $(R)$.
Assertion $(A):$
Polymerase chain reaction is used in $DNA$ amplification.
Reason $(R):$
The ampicillin resistant gene is used as a selectable marker to check transformation.
In the light of the above statements,choose the correct answer from the options given below:

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