(d)
Given, $\alpha$ and $\beta$ are different complex numbers and
$|\beta| = 1$
$\therefore\ \ \ \ \ \left| \frac{\beta - \alpha}{1 - \overline{\alpha}\beta} \right| = \frac{|\beta - \alpha|}{|\beta\overline{\beta} - \overline{\alpha}\beta|} = \frac{|\beta - \alpha|}{|\beta||\overline{\beta} - \overline{\alpha}|} = 1\ \$