This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Surgery
A 36-year female complaints of abdominal pain & constipation since 5 years. She has on & off rectal bleed when she tries to defecate forcefully. The most probable diagnosis is: 
Select and explain. 
A. Ulcerative colitis, B. Crohn's disease, C. Tuberculous intestine, D. Irritable bowel syndrome
D: Irritable bowel syndrome
Answer: D: Irritable bowel syndrome 
Explanation: The findings are consistent with irritable bowel syndrome. Crohn's disease would typically have perianal fistulae while ulcerative colitis has periods of acute disease and quiescent periods: the acute periods are severe and may lead to significant impairement.