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
If one wants to compare variation in two variables,which unit of measurement should be used 
Select and explain. 
A. Standard detion, B. Percentile, C. Variance, D. Coefficient of variance
D: Coefficient of variance
Answer: D: Coefficient of variance 
Explanation: Ref:Park's Textbook of Preventive and Social Medicine 25th Ed