A 26 year old man presented with abdomen distension and pain. His stools have been mucoid and sometimes blood stained. What is the most appropriate investigation?

The key is D. Barium meal. This is wrong key. Correct key is A. Stool C&S. [Probable diagnosis is Ulcerative colitis and abdominal distension may indicate toxic megacolon where barium enema should be avoided. Stool assessment is one of the lab procedures done in ulcerative colitis which may be the option from given ones. Stool culture is not confirmatory but suggestive].