The moment of inertia of a uniform flat disc about its own axis is I . The radius of the disc is a. A section ABCD of the disc (as shown in figure) is cut off and separated. The moment of inertia of the remaining part of the disc about the same axis will be :

• A

  $\frac{5}{6}\mathrm{I}$

• B

  $\frac{11}{12}\mathrm{I}$

• C

  $\frac{4}{5}\mathrm{I}$

• D

  $\frac{2}{3}\mathrm{I}$