Given below are two statements: One is labelled as Assertion $(A)$ and the other is labelled as Reason $(R)$.
Assertion $(A)$ : In a conical pendulum,angular momentum about its vertical axis remains constant.
Reason $(R)$ : Net torque about the vertical axis of a conical pendulum is not zero.
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.