The distance between the focus and directrix is, in this case, 8. Since the directrix is at x= something, the parabola opens sideways, and since the directrix is on the left, to the right. In which case, y^2=p(x), where p is 4 times distance of half of distance between directrix and focus. So, the answer is D. y^2=16x. The 4th answer.