Integrate the functions $$\frac{x^2}{\sqrt{x^6+a^6}}$$

Question

$\begin{array}{1 1} \frac{1}{3}\log\mid x^3+\sqrt{x^6+a^6}\mid+c. \\ \frac{1}{3}\log\mid x^6+\sqrt{x^6+a^6}\mid+c. \\ \frac{1}{6}\log\mid x^3+\sqrt{x^6+a^6}\mid+c. \\ \frac{1}{6}\log\mid x^6+\sqrt{x^6+a^6}\mid+c. \end{array}$