Answer: A) Stratified random sampling
Explanation:
Since , the researchers divided college students into the four classes (freshman, sophomore, junior, and senior) and then took a random sample of students from each class.
That means each category is participating in the sample.
It means , they used stratified sampling method where each class denotes a strata.
- Stratified random sampling is a kind of random sampling technique in which the researcher divides the whole population into some finite number of groups also known as strata , the he randomly pick individuals from each strata to make a sample.
Here , each category participates in researcher's analysis.
Hence, the correct answer is A) Stratified random sampling .