This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Epidemiology, Subject name: Social & Preventive Medicine
As compared to a routine case control study, nested case control study avoids problems (in study design) related to - 
Select and explain. 
A. Temporal association, B. Confounding bias, C. Need for long follow up, D. Randomization
A: Temporal association
Answer: A: Temporal association 
Explanation: A nested case-control (NCC) study is a variation of a case-control study in which cases and controls are drawn from the population in a fully enumerated coho. Usually, the exposure of interest is only measured among the cases and the selected controls. Thus the nested case-control study is more efficient than the full coho design.