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
Chronic subdural haematoma refers to collection present for a period of - 
Select and explain. 
A. 7 days, B. 6 months, C. 1 year, D. 21 days
D: 21 days
Answer: D: 21 days 
Explanation: None