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

All whole experiment is based on how quick the teenagers can run the 100m race with substantial amount of caffeine in there systems, thou she examines how fast the teenagers can run 100 m after taken enough amount of coffee unto there systems.

Independent variable is a type of variable that is constant, that is it does not depend on any variable, it is independent, it is constant, without this variable, nothing can be comprehensible.

The are very teenagers they are the subject of the experiment, without them she can't get the result she wants so teenagers are the constant variable.