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
[{'content': 'A most common site for squamous cell ca. esophagus is \nSelect and explain. \nA. Upper third, B. Middle third, C. Lower third, D. Gastro-esophageal junction.', 'role': 'user'}, {'content': 'Answer: B \nExplanation: Distribution of Squamous cell Ca\n\nUpper 1/3 - 10%\nMiddle 1/3 - 60%\xa0\xa0\xa0\xa0\xa0\xa0\xa0\xa0\xa0\nLower 1/3 - 30%', 'role': 'assistant'}]