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 40 yr old male patient presented with mild abdominal pain, mild constipation with a feeling of incomplete evacuation and mucus in stools for the past 4 years. On examination, tenderness is present in left iliac fossa. The most likely diagnosis is: 
Select and explain. 
A. Ulcerative colitis, B. Diverticular disease of the colon, C. Irritable bowel syndrome, D. Ca colon
C: Irritable bowel syndrome
Answer: C: Irritable bowel syndrome 
Explanation: None