The Essence of the Nonequivalent Control Group Design Is That

The essence of the nonequivalent control group design is that:

A) its validity remains unaffected even if both groups differ on some important variable before a study begins.
B) a comparable group of subjects is chosen and observed for the same period as the group for which a treatment is introduced.
C) when selecting groups on the basis of extreme scores on a pretest, a shift of posttest scores toward the less extreme values is because of the effect of a treatment.
D) groups are created based on the chronological ages of the participants at the time of a study.