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 3 groups. Group 1 receives a glass of water (zero caffeine). Group 2 receives the equivalent of 1 cups of coffee. Group 3 receives the equivalent of 2 cups of coffee. Each participant is then timed as they run he course. 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