Find the parametric form of normal for the circle $x^2+y^2=a^2$

Question

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