If $\tan \theta=\frac{1}{\sqrt{5}}$ and $\theta$ lies in the first quadrant, the value of $\cos \theta$ is :

  • A

    $\sqrt{\frac{5}{6}}$

  • B

    $-\sqrt{\frac{5}{6}}$

  • C

    $\frac{1}{\sqrt{6}}$

  • D

    $-\frac{1}{\sqrt{6}}$

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