Write the equation of conjugate hyperbola for the hyperbola $\large\frac{x^2}{a^2}-\frac{y^2}{b^2}$$=1$

Question

$\begin{array}{1 1}(a)\;-\large\frac{x^2}{a^2}+\frac{y^2}{b^2}\normalsize=1\\(b)\;\large\frac{x^2}{a^2}+\frac{y^2}{b^2}\normalsize=1\\(c)\;\large\frac{x^2}{a^2}-\frac{y^2}{b^2}\normalsize=1\\(d)\;\text{None of these}\end{array}$