$A$ round disc of moment of inertia $I_{2}$ about its axis perpendicular to its plane and passing through its centre is placed over another disc of moment of inertia $I_{1}$ rotating with an angular velocity $\omega$ about the same axis. The final angular velocity of the combination of discs is

• A
  $ \frac{I_{2}\omega}{I_{1} + I_{2}} $
• B
  $ \omega $
• C
  $ \frac{I_{1}\omega}{I_{1} + I_{2}} $
• D
  $ \frac{(I_{1} + I_{2})\omega}{I_{1}} $