An equilateral triangle is inscribed in the parabola $ y^2 = 4 ax$, where one vertex is at the vertex of the parabola. Find the length of the side of the triangle

Question

$\begin {array} {1 1} (A)\;3\sqrt 8 a & \quad (B)\;8\sqrt 3 a \\ (C)\;24a & \quad (D)\;None \end {array}$