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': 'Which of the following is the best method to know the  depth of invasion in esophageal carcinoma \nSelect and explain. \nA. Endoscopic ultrasound, B. CT, C. Contrast MRI, D. CECT', 'role': 'user'}, {'content': 'Answer: A \nExplanation: Ultrasound is used to know the t stage of cancer.', 'role': 'assistant'}]