27. As shown in the figure,
$$
A B \perp B C, B C \perp C D \text {, }
$$
$B C$ is tangent to the circle $O$ with $A D$ as the diameter. In which of the following cases is the area of $A B C D$ an integer?
(A) $A B=3, C D=1$.
(B) $A B=5, C D=2$.
(C) $A B=7, C D=3$.
(D) $A B=8, C D=4$.
(E) $A B=11, C D=5$.