Answer:
A. Stratification
Step-by-step explanation:
Stratified random sampling is used when the researcher wants to highlight a specific subgroup within an entire population.
Stratification technique is mainly used to reduce the population differences and to increase the efficiency of the estimates. In this method the population is divided into a number of subgroups or strata.
Each strata should be so formed such that they are homogeneous as far as possible.