Convert the Equation to Polar Form $x ^ { 2 } + y ^ { 2 } = 4$

Multiple Choice

Convert the equation to polar form. $x ^ { 2 } + y ^ { 2 } = 4$

A) $r ^ { 2 } = 4$
B) $4 r= \cos \theta + \sin \theta$
C) $y = 4 \cos \theta + 4 \sin \theta$
D) $r = 4$
E) none of these