$A$ disc with moment of inertia $I_1$ is rotating with an angular velocity $\omega$ about an axis passing through its center and perpendicular to its plane. Another disc with moment of inertia $I_2$ is placed on it,rotating about the same axis. What will be the combined angular velocity of both discs?

• A
  $\frac{I_2 \omega}{I_1 + I_2}$
• B
  $\omega$
• C
  $\frac{I_1}{I_1 + I_2} \omega$
• D
  $\frac{I_1 + I_2}{I_1} \omega$