Dr.Oishi is an educational psychologist interested in students' attitudes toward math and the effect of those attitudes on performance on standardized tests.He chooses his local school district to study.There are 15 middle schools,and he randomly chooses five.Then,of the 1,500 students in each of those five schools,he randomly recruits 250 students.This is an example of which of the following sampling techniques?
A)Snowball sample
B)Systematic sample
C)Multistage sample
D)Cluster sample

Multistage sampling technique: In psychological research, the term "multistage sampling technique" is described as one of the different sampling techniques an is referred to a "probability sampling technique" in which the sampling of participants or subjects being selected for a specific study is being carried out in various stages due to which the "sample size" being selected at the beginning of the research or study gets minimized at each ongoing stage. It is often considered as a "complex" type of cluster sampling.

In the question above, the given statement is an example of a multistage sampling technique.