This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Biostatistics, Subject name: Social & Preventive Medicine
One standard detion in normal standard curev includes value- 
Select and explain. 
A. 50%, B. 68%, C. 95%, D. 100%
B: 68%
Answer: B: 68% 
Explanation: Ref:Parks 23rd edition pg 849. 1SD : confidence limit = 68% 2SD : confidence limit = 95% 3SD : confidence limit = 99.7%