Ans: C. Stratified random samplingRef. Park 24/e p886, 23/e p850, 22/e p792; BK Malunan 6th/100-101).Stratified random sampling is used for selecting patients with respect to potential factors that will affect the results.Stratified random sample:The sample is deliberately drawn in a systematic way so that each poion of the sample represents corresponding strata of universe.This method is paicularly useful where one is interested in analyzing the data by a ceain characteristic of population, viz. Hindus, Christians, Muslims, age-groups etc.