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
Which of the following is the national level system that provides annual national as well as state level reliable estimation of feility and moality - 
Select and explain. 
A. Civil registration system, B. Census, C. Adhoc survey, D. Sample registration system
D: Sample registration system
Answer: D: Sample registration system 
Explanation: .