Let A and B be two distinct points on the parabola $$y^2 = 4x$$. If the axis of the parabola touches a circle of radius r having AB as its diameter, then the slope of the line joining A and B can be

A

$$-\frac{1}{r}$$

B

$$\frac{1}{r}$$

C

$$\frac{2}{r}$$

D

$$-\frac{2}{r}$$