Why Do the Groups Have to Be Equivalent at the Start

Multiple Choice

Why do the groups have to be equivalent at the start of an experiment?

A) If the groups are not equivalent at the start of an experiment, the experiment is contaminated by ethnocentrism.
B) If the groups are not equivalent at the start of an experiment, demand characteristics are more likely.
C) If the groups are not equivalent at the start of an experiment, it is impossible to conduct a replication.
D) If the groups are not equivalent at the start of an experiment, we cannot be certain that the IV caused any difference observed in the DV.