Cosella Is Conducting an Experiment Where She Assesses How Quickly

Multiple Choice

Cosella is conducting an experiment where she assesses how quickly teenagers can run a 100-meter race after consuming specific amounts of caffeine. She divides her sample up into three groups. Group 1 receives a glass of water (zero caffeine) . Group 2 receives the equivalent of the caffeine in one cup of coffee. Group 3 receives the equivalent of two cups of coffee. Each participant is then timed as they run the course. In this study, the independent variable is

A) the previous running experience of each participant.
B) the teenagers who are being studied.
C) the time it takes to run the 100-meter race.
D) the amount of caffeine being ingested.