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 $\cos \omega t$ ($\omega \ne {\omega }_0$) is applied to the oscillator. The displacement of the oscillator will be proportional to:

1. A
   $\frac{m}{{\omega }_0^2-{\omega }^2}$
2. B
   $\frac{1}{m({\omega }_0^2-{\omega }^2)}$
3. C
   $\frac{1}{m({\omega }_0^2+{\omega }^2)}$
4. D
   $\frac{m}{{\omega }_0^2+{\omega }^2}$