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
Calculated positive predictive value of ELISA test for HIV with sensitivity 99%, specificity 99% , prevalence of HIV in population 5/1000 ? 
Select and explain. 
A. 10, B. 70, C. 33, D. All
C: 33
Answer: C: 33 
Explanation: Ans. is 'c' i.e., 33