The vertex of a parabola is the point `(a , b)` and the latus rectum is of length `ldot` If the axis of the parabola is parallel to the y-axis and the parabola is concave upward, then its equation is (a) `(x+a)^2=l/2(2y-2b)` (b)`(x-a)^2=l/2(2y-2b)` (c) `(x+a)^2=l/4(2y-2b)` (d) `(x-a)^2=l/8(2y-2b)`