Given below are two statements: one is labelled as Assertion (A) and the other is labelled as Reason (R).
Assertion (A) : The radius vector from the Sun to a planet sweeps out equal areas in equal intervals of time and thus areal velocity of planet is constant.
Reason (R) : For a central force field the angular momentum is a constant.
In the light of the above statements, choose the most appropriate answer from the options given below :

• Correct answer
  A

  Both $(\mathrm{A})$ and $(\mathrm{R})$ are correct and $(\mathrm{R})$ is the correct explanation of $\mathrm{( A)}$
• B

  Both $(\mathrm{A})$ and $(\mathrm{R})$ are correct but $(\mathrm{R})$ is not the correct explanation of (A)
• C

  (A) is correct but $(\mathrm{R})$ is not correct
• D

  (A) is not correct but (R) is correct

Hence, the correct answer is option: 'A'.