What is the equation of the parabola, whose vertex and focus are on the x-axis at distance a and b from the origin respectively ?
(b>a>0)

A. y²=8(b−a)(x−a)
B. y²=4(b+a)(x−a)
C. y²=4(b−a)(x+a)
D. y²=4(b−a)(x−a)