Choosing an Antiderivative In Exercises $1-4,$ select the correct antiderivative.
$\frac{d y}{d x}=\frac{x}{x^{2}+1}$
$$
\begin{array}{ll}{\text { (a) } \ln \sqrt{x^{2}+1}+c} & {\text { (b) } \frac{2 x}{\left(x^{2}+1\right)^{2}}+c} \\ {\text { (c) arctan } x+c} & {\text { (d) } \ln \left(x^{2}+1\right)+c}\end{array}
$$