Which value of $x$ will make the fraction undefined ?<br> $\qquad \qquad \qquad \large\frac{x^2}{9x^2-1}$

Question

$\begin{array}{1 1} (a)\;\frac{1}{3} \\ (b)\;\frac{-1}{3} \\ (c)\;\pm \frac{1}{3} \\(d)\;0 \end{array}$