Answer:
The correct answer is:
stratified sampling
Explanation:
Stratified sampling is a type of sampling method where the population to be sampled is divided into subgroups or strata and then random selection is made, and these strata are formed based on some shared common characteristics. In this example, the population to be sampled is a population of professors, but the researcher went further to divide this group into professors, assistant professors, associate professors, adjunct professors, and visiting profesors.