To determine the effects of caffeine on alertness, Dr. Clinton has 50 children consume caffeine, while 50 others do not receive caffeine. In order for Dr. Clinton to be able to determine cause-and-effect, she must insure that
A) her participants do not have any choice in whether to participate in the experiment.
B) all of her participants currently consume caffeine.
C) her participants have about equal amounts of alertness.
D) her participants are randomly assigned to view one of the two groups.
D
Psychology
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