If a normal to $\mathrm{y}^{2}=4 \mathrm{ax}$ makes an angle $\theta$ with the positive direction of $\mathrm{x}$ -axis, perpendicular distance of it from a tangent parallel to it is
(a) a $\operatorname{cosec}^{2} \theta \sec \theta$
(b) a $\operatorname{cosec} \theta \sec \theta$
(c) a $\operatorname{cosec} \theta \sec ^{2} \theta$
(d) a $\operatorname{cosec} \theta \sec ^{3} \theta$