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: Social & Preventive Medicine
Standard error of mean is calculated by 
Select and explain. 
A. SD/n, B. SD/mean, C. SD/-1/1, D. Mean/SD
C: SD/-1/1
Answer: C: SD/-1/1 
Explanation: SD/ 1/7 Standard error of mean = SD/j SD - standard detion n - number of samples