Is hand span a good predictor of how much candy you can grab? Using 45 volunteer college students as subjects, researchers set out to explore whether a linear relationship exists between hand span (cm) and the number of Tootsie Rolls each subject could grab.

Is this an observational study or a randomized experiment?

a. Observational study, because the number of tootsie rolls grabbed was not randomly assigned.

b. Observational study, because hand span was not randomly assigned.

c. Observational study, because these are volunteers, not a random sample.

d. Randomized experiment, because the researchers are investigating a relationship between two variables.