The triangle `P Q R` of area `A` is inscribed in the parabola `y^2=4a x` such that the vertex `P` lies at the vertex of the parabola and the base `Q R` is a focal chord. The modulus of the difference of the ordinates of the points `Qa n dR` is `A/(2a)` (b) `A/a` (c) `(2A)/a` (d) `(4A)/a`