Answer:
systemic sampling
Step-by-step explanation:
Convenience sampling is when the data is taken from a specific group because it is easier or more convenient for the researcher.
Systematic sampling is when the samples are taken according to a specific or fixed rule.
Cluster and stratified sampling are when the population is divided into small groups according to the goal of the study.
Therefore, the method used in this case is systematic sampling, because the fixed rule or interval is to select every third person on the list.