The tangent PT and the normal PN to the parabola y2 = 4ax at a point P on it meet its axis at points T and N, respectively. The locus of the centroid of the triangle PTN is a parabola whose
(a) vertex is (2a/3,0) (b) directrix is x = 0 (c) latusrectum is 2a/3 (d) focus is (a, 0)
