Consider an experiment designed to see whether cash incentives can improve school attendance. The researcher chooses two groups of 100 high school students: She offers one group $10 for every week of perfect attendance. She tells the other group that they are part of an experiment but does not give them any incentive. The students who do not receive an incentive represent:

(a) the treatment group; (b)

the control group;

(c) the observation group.