Which of the following describes the graph of x2+y2=9x^2 + y^2 = 9x2+y2=9?
A circle with center (0,0)(0,0)(0,0) and radius 333
A circle with center (0,0)(0,0)(0,0) and radius 999
An ellipse with center (0,0)(0,0)(0,0)
A parabola opening upward