Form the differential equation of the family of circles having centre on $y$-axis and radius $3$ units.

Question

$\begin{array}{1 1} (A)\;(x^2 - 9)(y')^2 + x^2 = 0 \\ (B)\;(x^2 - 9)(y')^2 - x^2 = 0 \\ (C)\;(x^2 - 9)(y')^2 + x^3 = 0 \\ (D)\;(x^2 - 9)(y')^2 + x^4 = 0 \end{array}$