An equilateral triangle is inscribed in the parabola $\mathrm{y}^{2}=4 \mathrm{ax}$ such that one of the vertices is the vertex of the parabola. Then the length of each side is
(a) $\mathrm{a} \sqrt{3}$
(b) $8 \mathrm{a} \sqrt{3}$
(c) $4 \mathrm{a} \sqrt{3}$
(d) $2 \mathrm{a} \sqrt{3}$