Reynaldo is reviewing a study on the effectiveness of a new drug-free remedy for depression. in the study, a group of participants was given a natural supplement for a period of six weeks. they rated their mood both before and after treatment. two-thirds of the group reported a marked improvement after the trial. what change in this study would do the most to increase reynaldo's confidence that sound scientific practices were followed?
a. including a control group that did not receive the supplement.
b. including information about the manufacturer and cost of the supplement.
c. including testimony of participants in the study's documentation.
d. including more details about the self-reported mood ratings