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
Area under standard normal distribution curve is 
Select and explain. 
A. 1, B. 0.5, C. 5, D. 2
A: 1
Answer: A: 1 
Explanation: Standard normal distribution curve has :

Area under the curve = 1.
Has variance = 1.
Mean = median = mode.
Mean = 0
Standard deviation = 1.