Ans: B. Case controlstudy(Ref: Park 24/e p76, 23Ie p71; 22/c p76).Best study design to assess in quick time the strength of association between smoking and lung cancer is case control study.Permanent method of epidemiological investigation.Case control studies, often called retrospective studies are a common first approach to test causal hypothesis.Distinct features:Both exposure and outcome (disease) have occurred before the sta of study.Study proceeds backwards from effect to cause.Uses a control or comparison group to suppo or refute an inference.