This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: G.I.T, Subject name: Surgery
[{'content': "In classic Barret's, the length of columnar epithelium in distal oesophagus is \nSelect and explain. \nA. >1cm, B. >2cm, C. >3cm, D. >4cm", 'role': 'user'}, {'content': "Answer: C \nExplanation: Classic Barrett's (>= 3cm columnar epithelium);Sho-segment Barrett's (<3 cm of columnar epithelium);Cardia metaplasia (intestinal metaplasia at the oesophagogastric junction without any macroscopic change at endoscopy).The relative risk of cancer rises with increasing length of abnormal mucosa.", 'role': 'assistant'}]