2010 AMC 10B Problem 6

A circle is centered at O, \overline{AB} is a diameter and C is a point on the circle with \angle COB = 50^\circ. What is the degree measure of \angle CAB?

\textbf{(A)}\ 20 \qquad \textbf{(B)}\ 25 \qquad \textbf{(C)}\ 45 \qquad \textbf{(D)}\ 50 \qquad \textbf{(E)}\ 65

Full credit goes to MAA for authoring these problems. These problems were taken on the AOPS website.