$\int\left(1+\tan ^2 x\right)(1+2 x \tan x) d x=$

• A

  $x \sec x+\mathrm{c}$
• B

  $x \tan ^2 x+\mathrm{c}$
• Correct answer
  C

  $x \sec ^2 x+\mathrm{c}$
• D

  $x \tan x+\mathrm{c}$

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