Final answer:
The correct answer is option A, because the data set contains the height measurements of all students in the designated classroom, representing the entire population for the study, not just a sample.
Step-by-step explanation:
The correct answer is option A. Population, because it is a collection of heights for all students in the classroom. A population is defined as the entire group that is the subject of a study. In this case, if the study or research is focused on the students within a specific classroom and we are measuring the height of each student therein, we are dealing with the whole set of data that pertains to our research subjects—the classroom students. This is what constitutes a population.
In contrast, a sample would be a subset of the population, which is used to make inferences about the population as a whole. Going back to our scenario, if we were to study a larger set, such as all students in the school, and we only measured the heights of students in one classroom to represent the school, then this classroom would constitute a sample.