This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: C.N.S., Subject name: Medicine
[{'content': 'A patient with history of weakness of one side was brought to AIIMS emergency medicine department with altered sensorium. A CT was taken, and showed the following. What should be done next? \nSelect and explain. \nA. Decompressive craniotomy, B. Intravenous mannitol, C. Observe and follow-up, D. Aspirin', 'role': 'user'}, {'content': 'Answer: B \nExplanation: ANS. B', 'role': 'assistant'}]