The equation of a circle is defined as
[tex]\begin{gathered} x^2+y^2=r^2 \\ \text{where} \\ r\text{ is the radius} \end{gathered}[/tex]Given that the radius of the circle is 2, then the equation of the circle is
[tex]x^2+y^2=2^2\text{ (option C)}[/tex]Which can then be simplified to
[tex]x^2+y^2=4\text{ (option D)}[/tex]And we can rearrange the equation
[tex]x^2-4=-y^2\text{ (option A)}[/tex]Which means that it cannot be the equation
[tex]x^2+4=-y^2[/tex]