Simplify for the rational expression : $\large \frac{9x^2-1}{(3x+1)(3x-1)}$

Question

$\begin{array}{1 1} (a)\;1 \\ (b)\;\large\frac{1}{3x+1} \\ (c)\;3x-1 \\(d)\;\frac{1}{3x-1} \end{array}$