If the direction cosines of two lines satisfy the equations $2 l+m-n=0$, $l^2-2 m^2+n^2=0$ and $\theta$ is the angle between the lines then $\cos \theta=$

• Correct answer
  A

  $\frac{1}{5}$
• B

  $\frac{\pi}{4}$
• C

  $\frac{2}{3}$
• D

  $\frac{\pi}{3}$

Hence, the correct answer is option: 'A'.