Answer:
B. Stratified sampling, because there are specific subgroups to investigate.
Explanation:
Stratified Sampling is a sampling method and is used when the population has subgroups with different characteristics. Random sampling is applied in each of the sub-groups proportional to their size and then these samples combined together to create sample of the study.
Since there are three towns with people from different occupations ( retirees,business owners, office workers), it is better to use stratified sampling method.