Dr. Longman wanted to know about the effect of light on work performance. She changed the lights for one group and left the lights the same for another. She was doing a (n):

A. correlational study.

B. naturalistic observation.

C. survey.

D. experiment.

Dr. Longman is doing A. correlational study. She wants to test the relationship between lighting and work performance in two variables. The first variable uses the same lighting as the usual, while the other variable is changed to a different lighting. The results of the two variables will then be evaluated whether there is a substantial increase or decrease between them.