If P1P2 and Q1Q2, two focal chords of a parabola y2=4ax at right angles, then
a. area of the quadrilateral P1Q1P2Q2 is minimum when the chords are inclined at an angle π/4 to the axis of the parabola.
b. minimum area is twice the area of the square on the latusrectum of the parabola.
c. minimum area of quadrilateral P1Q1P2Q2 cannot be found.
d. minimum area is thrice the area of the square on the latusrectum of the parabola.