$A$ particle of mass $m$ is attached to a spring (of spring constant $k$) and has a natural angular frequency $\omega_0$. An external force $F(t)$ proportional to $\cos \omega t$ (where $\omega \neq \omega_0$) is applied to the oscillator. The displacement of the oscillator will be proportional to:

• A
  $\frac{m}{\omega_0^2 - \omega^2}$
• B
  $\frac{1}{m(\omega_0^2 - \omega^2)}$
• C
  $\frac{1}{m(\omega_0^2 + \omega^2)}$
• D
  $\frac{m}{\omega_0^2 + \omega^2}$