A complex number z is said to be unimodular if $|z|=1$ .Suppose $z_1$ and $z_2$ are complex number Such that $\large\frac{z_1 -2 z_2}{2-z_1z_2}$is unimodular and $z_2$ is not unimodular . Then the point $Z_1$ lies on a :

Question

$\begin{array}{1 1} \text{Straight line parallel to x-axis} \\ \text{Straight line parallel to y-axis} \\ \text{circle of radius 2 } \\\text{circle of radius } \sqrt{2} \end{array}$