As shown in the figure,two blocks of masses $m_1$ and $m_2$ are connected to a spring of force constant $k$. The blocks are slightly displaced in opposite directions to $x_1$ and $x_2$ distances and released. If the system executes simple harmonic motion,then the angular frequency of oscillation of the system $(\omega)$ is:

• A
  $\left(\frac{1}{m_1}+\frac{1}{m_2}\right) k^2$
• B
  $\sqrt{\left(\frac{1}{m_1}+\frac{1}{m_2}\right) k^2}$
• C
  $\sqrt{\left(\frac{1}{m_1}+\frac{1}{m_2}\right)}$
• D
  $\sqrt{\left(\frac{1}{m_1}+\frac{1}{m_2}\right) k}$