Answer:
D. Cluster sampling
Explanation:
Dealing with the whole population can be cumbersome, time-consuming and very expensive. In order to make it more feasible for researchers they can employ cluster sampling. In cluster sampling, the population are divided into precincts, or gropus. The researcher then selects the groups that will be included in the study through simple random samping or systematic sampling. The researcher can opt to choose let the whole cluster or group to participate in the study or they can randomly select the individuals within the groups.