Answer:
Multistage Sampling.
Step-by-step explanation:
Multistage Sampling -
It is the method of sampling , where samples are taken in small portion , at every level of the sampling process , is referred to as multistage sampling.
It is quite a complex method , which require dividing the population into groups , and then further sampling is done, hence it is a long process and require a lot of time.
Hence, from the question, the type of sampling method involved in the question is multistage sampling.