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
In a normal curve, the area of one standard deviation around the mean includes which of the following per cent of values in a distribution - 
Select and explain. 
A. 0.486, B. 0.683, C. 0.954, D. 0.997
B: 0.683
Answer: B: 0.683 
Explanation: None