Answer: He used cluster sampling method and Option 'C' is correct.
Step-by-step explanation:
Cluster is a type of sampling method in which we divide the population into clusters and then sample of clusters is being chosen among them.
Stratified is a type of sampling method in which the researches divides the population into different strata, then randomly chosen the final subject proportionally among the strata.
Systematic is a type of sampling method in which members from a larger population are chosen based on random starting point but it has fixed and periodic interval systematically.
Convenience is a type of sampling method that is non probability sampling method as it is chosen which is close to hand.
According to question, we have an education researcher randomly selects 48 middle schools from across the country and interviews every teacher at each of the selected schools.
So, it forms a cluster in which sample of clusters is being chosen from selected school.
Hence, he used cluster sampling method.
Thus, Option 'C' is correct.
