Final answer:
In a video game study, a professor randomly selected fifty boys from various high schools to represent a smaller group that is being studied. These boys make up the sample of the study.
Step-by-step explanation:
In this video game study, the professor randomly selected fifty boys from various high schools. These fifty boys represent a smaller group that is being studied, so they make up the sample of the study. A sample is used because the population of teenage boys is too large to involve every member in the experiment. Therefore, the correct answer is a) Sample.