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: Radiology
[{'content': 'Barium swallow is used for \nSelect and explain. \nA. Esophagus, B. Colon, C. Duodenum, D. Jejunum', 'role': 'user'}, {'content': 'Answer: A \nExplanation: The esophagus is a muscular tube connecting the throat (pharynx) with the stomach.\nThe esophagus is about 8 inches long and is lined by moist pink tissue called mucosa.\nThe esophagus runs behind the windpipe (trachea) and heart, and in front of the spine.', 'role': 'assistant'}]