20. In quadrilateral $\mathrm{ABCD}$, $\angle B=90^{\circ}$, and $A B=B C=5, C D=2 \sqrt{15}, D A=\sqrt{10}$, the degree measure of $\angle B A D$ is
(A) $90^{\circ}$
(B) $120^{\circ}$
(C) $135^{\circ}$
(D) $150^{\circ}$