The stratified method is a method of sampling from a population that can be divide in subgroups called subpopulations. Following this definition, the first choice would be an example of stratified method since each classe would represent a subpopulation.
The cluster method is a method of sampling which consists in dividing the population into clusters to then choose one cluster randomly to carry out the study. The second choice would be an example of this sampling method since they made up 4 different classes of students to then select a random sample.
The random method is a method of sampling which consits in