Subjects are said to be assigned randomly when a. every subject has an equal chance of being assigned to either the experimental or control group. b. each subject is selected to participate in an experiment from a sample that is representative of the larger population. c. each subject is assigned to experimental and control groups in such a way that the groups differ on some critical variable before the experiment begins. d. neither the experimenter nor the subject knows whether the subject is in the experimental or control group.