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
For calculation of sample size for a prevalence study all of the following are necessary except 
Select and explain. 
A. Prevalence of disease in population, B. Power of the study, C. Significance level, D. Desired precision
D: Desired precision
Answer: D: Desired precision 
Explanation: Sample size depends upon:

The effect size (usually the difference between 2 groups).
The population standard deviation (for continuous data).
The desired power of the experiment to detect the postulated effect (Power = 1 – b)
The significance level.