If $\mathrm{I}_n=\int \frac{1}{\left(x^2+1\right)^n} d x$, then $2 n \mathrm{I}_{n+1}-(2 n-1) \mathrm{I}_n=$

• A

  $\frac{\left(x^2+1\right)^n}{x}+\mathrm{c}$
• Correct answer
  B

  $\frac{x}{\left(x^2+1\right)^n}+c$
• C

  $x\left(x^2+1\right)^{n-1}+c$
• D

  $\frac{x}{\left(x^2+1\right)^{n-1}}+\mathrm{c}$

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