In a Study Comparing Two Nonequivalent Groups, a Selection-History Confound

Multiple Choice

In a study comparing two nonequivalent groups, a selection-history confound occurs when

A) some event intervenes between pretest and posttest and affects just one of the groups.
B) some event intervenes between pretest and posttest and affects both selected groups equally.
C) selection influences one of the groups and history influences the other.
D) some historical event causes a failure of the random assignment procedure.