Dr Shang Is Studying the Effects of Caffeine on Hunger

Dr. Shang is studying the effects of caffeine on hunger. He hypothesizes that people who ingest more caffeine experience less hunger pangs throughout the day. He designs a study where one group of participants is given caffeine throughout the day, and the other group is not allowed to have any caffeine. He then has the two groups journal their hunger pangs throughout the day and he compares the results. In this study, the independent variable is the:

A) number of hunger pangs a participant experiences.
B) amount of caffeine a person ingests.
C) time of day when the hunger pangs happen.
D) age of the participant.