Find the Center-Radius Form of the Equation of the Circle $( 0,0 )$

Multiple Choice

Find the center-radius form of the equation of the circle.
-center $( 0,0 )$ , radius 3

A) $x ^ { 2 } + y ^ { 2 } = 9$
B) $x ^ { 2 } + y ^ { 2 } = 3$
C) $x ^ { 2 } + y ^ { 2 } = \sqrt { 3 }$
D) $x ^ { 2 } + y ^ { 2 } = 6$