This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Biostats, Subject name: Social & Preventive Medicine
The mean of the 25 patients' plasma volumes is 12.5 litres. Standard detion is 0.25. Calculate standard error 
Select and explain. 
A. 0.05, B. 0.5, C. 0.01, D. 0.1
A: 0.05
Answer: A: 0.05 
Explanation: S.E = S/[?]n S = Standard detion = 0.25 n = sample size = 25 S.E. = 0.25/[?] 25 = 0.25/5 = 0.05