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': "Color of hand change to following color, when a patient of Raynaud's disease puts his hand in cold water: \nSelect and explain. \nA. White, B. Yellow, C. Blue, D. Black.", 'role': 'user'}, {'content': 'Answer: A \nExplanation: None', 'role': 'assistant'}]