Find the Standard Form of the Equation of the Parabola $= 18$

Multiple Choice

Find the standard form of the equation of the parabola.
-Vertex at the origin, opens downward, focal width $= 18$

A) $x ^ { 2 } = 18 y$
B) $x ^ { 2 } = - 18 y$
C) $y ^ { 2 } = - 4.5 x$
D) $y ^ { 2 } = 18 x$