The tangent PT and the normal PN to the parabola y2 = 4ax at a point P on it meet its axis at point 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. latus rectum is 2a/3
d. focus is (a, 0)
