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: Dental
Standard Deviation (SD) formula 
Select and explain. 
A. Highest X-lowest X/2, B. Σ(X-X)/n, C. Σ(X-X)2/n, D. Σ(X-X)2/n-1
C: Σ(X-X)2/n
Answer: C: Σ(X-X)2/n 
Explanation: None