Does St John's Wort Have a Significant Effect in Treating Major

Multiple Choice

Does St. John's wort have a significant effect in treating major depression? A study looked at 340 adult outpatients suffering from major depression as measured by their HAM-D score, randomly assigning each subject to either a placebo, St. John's wort, or a second active treatment for comparison.
Why is this study an experiment? Because:

A) the researchers were comparing outcomes from three groups.
B) there is a response variable.
C) there was a placebo.
D) the researchers assigned treatments to the subjects.