Dr. Hernandez wants to examine the impact of caffeine on test performance. She randomly assigns the 60 students in her class to three groups (no caffeine-placebo, 100mg of caffeine, 200mg of caffeine) and then 40 minutes later students take a test. What kind of study is this?
a. A quasi-experimental study
b. A correlational study
c. An experimental study
d. A regression-based study
e. A lab based observational cross sectional study