In the Context of Experimental Research,the Logic of Random Assignment

In the context of experimental research,the logic of random assignment is that

A) if participants in an experiment are assigned to each group by stratification,the actual differences between the groups will sustain over the long run.
B) if participants in an experiment are assigned to each group only by chance,the actual similarities between the groups will sustain over the long run.
C) if participants in an experiment are assigned to each group by stratification,the potential differences between the groups will cancel out over the long run.
D) if participants in an experiment are assigned to each group only by chance,the potential differences between the groups will cancel out over the long run.