$\tan \left(2 \operatorname{Tan}^{-1}\left(\frac{1}{3}\right)+\operatorname{Tan}^{-1}\left(\frac{1}{7}\right)\right)=$

• A

  $\frac{1}{\sqrt{3}}$
• B

  $\sqrt{3}$
• Correct answer
  C

  $1$
• D

  $3 / 7$

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