If  $\theta$ is an angle given by $\cos \theta =\frac{{\cos }^2\alpha +{\cos }^2\beta +{\cos }^2\gamma }{{\sin }^2\alpha +{\sin }^2\beta +{\sin }^2\gamma }$ where $\alpha ,\beta ,\gamma$ are the angles made by a line with the axes $\overrightarrow{OX},\overrightarrow{OY},\overrightarrow{OZ}$respectively then the value of $\theta$ is

• A

  $\frac{\pi }{3}$

• B

  $\frac{\pi }{6}$

• C

  $\frac{\pi }{2}$

• D

  $\frac{\pi }{4}$