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: Pathology
[{'content': 'Salivary secretion becomes zero at: \nSelect and explain. \nA. >30 Gray, B. >60 Gray, C. >40 Gray, D. >50 Gray', 'role': 'user'}, {'content': 'Answer: B \nExplanation: None', 'role': 'assistant'}]