An Experimenter Studying the Over Justification Effect Wants to Compare

An experimenter studying the over justification effect wants to compare the behaviour of students who are rewarded for doing an enjoyable task with that of students who are not rewarded. For each student, he decides which condition they will be in by flipping a coin. This procedure

A) ensures that each student has an equal chance of being in either condition.
B) does not ensure that a random sample of participants will be selected.
C) helps to rule out initial group differences as a potential cause of the experimental effects.
D) all of the choices are correct.