In the following figure, MN is a tangent to a circle with centre O at point A. If BC is a diameter and $$\angle ABC = 42^{\circ}$$, then find the measure of $$\angle$$ MAB.

A

$$84^{\circ}$$

B

$$42^{\circ}$$

C

$$48^{\circ}$$

D

$$45^{\circ}$$