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: Anatomy
[{'content': 'The toughest layer of the esophagus is the \nSelect and explain. \nA. Mucosa, B. Submucosa, C. Muscularis, D. Adventitia', 'role': 'user'}, {'content': 'Answer: C \nExplanation: C i.e. Muscularis Muscularis externa is the toughest layer of esophagusQ; upper 1/3rd is composed of skeletal muscleQ, lower 1/3rd is composed of smooth muscleQ & the middle third is made up of both types of muscle.', 'role': 'assistant'}]