Indicate Whether the Study Described Is an Observational Study or a Controlled

Indicate whether the study described is an observational study or a controlled experiment.
-Researches want to find out which U. S. movie has the most positive audience reaction for the current week. As they exited a randomly selected movie theater, movie-goers were asked to give the movie they had just viewed a letter grade of A, B, C, D, or F. In this scenario, the movie-goers
Are an example of a_{--------------------} .

A) Population
B) Sample
C) Variable