Cities A, B, C, D, and E are connected by roads \widetilde{A B}, \widetilde{A D}, \widetilde{A E}, \widetilde{B C}, \widetilde{B D}, \widetilde{C D}, and \widetilde{D E}. How many different routes are there from A to B that use each road exactly once? (Such a route will necessarily visit some cities more than once.)
Answer Choices
A. 7
B. 9
C. 12
D. 16
E. 18