Answer:
c. Cluster sampling
Step-by-step explanation:
Cluster sampling is a kind of sampling whereby the entire population is divided into different groups(clusters) from which simple random samples are selected from these clusters to conduct the analysis. If possible, all the individual in the selected clusters are sampled.
For the case above, Christine samples the population by dividing the residents by towns(clusters) and randomly selecting 9 of the towns(9 selected clusters). The type of sampling used is Cluster sampling. Since it involves dividing the population into clusters, and sampling the selected clusters.