Given below are two statements: one is labelled as Assertion $A$ and the other is labelled as Reason $R$.
Assertion $A$: Moment of inertia of a circular disc of mass $M$ and radius $R$ about $X, Y$ axes (passing through its plane) and $Z$-axis which is perpendicular to its plane were found to be $I_{x}, I_{y}$ and $I_{z}$ respectively. The respective radii of gyration about all the three axes will be the same.
Reason $R$: $A$ rigid body making rotational motion has fixed mass and shape.
In the light of the above statements,choose the most appropriate 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 not correct but $R$ is correct.
• C
  $A$ is correct but $R$ is not correct.
• D
  Both $A$ and $R$ are correct and $R$ is the correct explanation of $A$.