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.
-A group of students is divided into two groups. One group listens to classical music while taking a math test and the other group takes the test in silence. The average test scores of the two groups are compared to see whether listening to music during a math test has an effect on scores.

A) Controlled experiment
B) Observational study