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': 'Prognosis for carcinoma rectum is best assessed by ? \nSelect and explain. \nA. Site of tumour, B. Histological grading, C. Size of tumours, D. Duration of the symptoms', 'role': 'user'}, {'content': "Answer: B \nExplanation: Ans. is 'b' i.e., Histological grading", 'role': 'assistant'}]