Which of the following is true concerning inflammatory bowel disease (IBD):   A. It is always easy to tell the difference between Crohn's and ulcerative colitis B. Only ulcerative colitis is associated with an increased risk of cancer C. Fistulae and transmural inflammation are characteristic of Crohn's Disease D. Restorative proctocolectomy is contraindicated in ulcerative colitis E. Autoimmunity does not contribute to IBD