In triangle ABC, AC \equal{} CD and \angle CAB \minus{} \angle ABC \equal{} 30^\circ. Then ∠BAD is:
[asy]defaultpen(linewidth(.8pt));
unitsize(2.5cm);
pair A = origin;
pair B = (2,0);
pair C = (0.5,0.75);
pair D = midpoint(C--B);draw(A--B--C--cycle);
draw(A--D);label("A",A,SW);
label("B",B,SE);
label("C",C,N);
label("D",D,NE);[/asy]<spanclass=′latex−bold′>(A)</span>30∘<spanclass=′latex−bold′>(B)</span>20∘<spanclass=′latex−bold′>(C)</span>2221∘<spanclass=′latex−bold′>(D)</span>10∘<spanclass=′latex−bold′>(E)</span>15∘