Find an Equation of the Line, and Write It in (A)

Multiple Choice

Find an equation of the line, and write it in (a) slope-intercept form if possible and (b) standard form.
-Through $(3,9)$ ; horizontal

A) (a) not possible
(b) $x=3$
B) (a) not possible
(b) $x=-9$
C) (a) $y=-3$
(b) $y=-3$
D) (a) $y=9$
(b) $y=9$