Which of the Following Studies Used a Single-Factor, Nonequivalent Groups

Which of the following studies used a single-factor, nonequivalent groups design?

A) Kroeger et al.'s study, which evaluated the effects of a social skills program for autism
B) the study by Kasser and Sheldon, which compared groups writing two kinds of essays
C) Lee and Aronson's study comparing the effects of having a room move forward or backward
D) the study by McDonald and Flanagan, which examined the effects of traumatic brain injury