Early studies into the effectiveness of "sleep learning" tapes

suggested that learning could indeed occur if a tape was played while a subject was asleep. These studies failed, however, to monitor the electrical activity of the participants' brains, and thus did not consider the possibility that the tapes had actually awakened these individuals. This alternative explanation for the findings is consistent with the critical thinking concept of
A) extraordinary claims.
B) ruling out rival hypotheses.
C) replicability.
D) correlation versus causation.

Answer: B