Which statement is true about the curve defined by $x^2+y^2=49$?

It is an ellipse centered at $(7,0)$ because the variables have the same coefficients

It is a circle centered at the origin with radius $7$

It does not represent any points unless $49$ is written as $R^2$, since the constant term must be zero for a circle centered at the origin

It is a parabola because $x^2+y^2$ can be rearranged to express $y\left(x\right)$