Let us begin by defining each type of sampling
Stratified sampling is a method of sampling from a population that can be partitioned into subpopulations.
In cluster sampling, researchers divide a population into smaller groups known as clusters. They then randomly select among these clusters to form a sample.
Convenience sampling (also known as grab sampling, accidental sampling, or opportunity sampling) is a type of non-probability sampling that involves the sample being drawn from that part of the population that is close to hand.
A voluntary response sample can be defined as a sample made up of participants who have voluntarily chosen to participate as a part of the sample group.
The researcher in this problem selected 2 random busloads of students. This sample can be further divided into subpopulations.
Answer: Stratified sampling
