In an Experiment to Study the Effects of Caffeine on Performance

Multiple Choice

In an experiment to study the effects of caffeine on performance, an experimenter asked the male students in an introductory psychology class to drink two regular Pepsis before a test and the female students to drink two caffeine-free Pepsis. She then compared performance of the two groups on the test. A confounding variable in this study is:

A) whether participants had studied for the test.
B) the type of drink.
C) the gender of the participants.
D) the amount of caffeine in the Pepsi.