Triangles A B C and A D C are isosceles with A B=B C and A D=D C. Point D is inside \triangle A B C, \angle A B C=40^{\circ}, and \angle A D C=140^{\circ}. What is the degree measure of \angle B A D ?

**Answer Choices**

A. 20

B. 30

C. 40

D. 50

E. 60