Calculate the moment of inertia of a disc about an axis tangent to its inner circle and lying in the plane of the disc. The mass of the disc is $M$,the inner radius is $R_1$,and the outer radius is $R_2$.

• A
  $\frac{M}{4}(R_1^2 + R_2^2) + MR_1^2$
• B
  $M(R_1^2 + R_2^2) + MR_1^2$
• C
  $\frac{M}{4}(R_1^2 - R_2^2) - MR_1^2$
• D
  $\frac{M}{4}(R_1^2 + R_2^2) - MR_1^2$