Wilhelm and Colleagues (2011) Had Participants Memorize a List of Word

Wilhelm and colleagues (2011) had participants memorize a list of word pairs and subsequently recall them after equivalent periods of either sleep or wakefulness. Immediately after the initial memorization, half of the participants in both groups were told that they would be tested on these word pairs later. Which statement accurately summarizes the major finding of this study?

A) Participants who slept after memorizing the word pairs usually recalled more word pairs than those who stayed awake.
B) There was no difference in memory recall after sleep or an equivalent period of wakefulness, so long as participants in the wakefulness group did not encounter distracting information in the interim between memorization and recall.
C) Participants who slept after memorizing the word pairs recalled more than those who stayed awake, but only when they were not aware that they would be tested on this information.
D) Participants who slept after memorizing the word pairs recalled more than those who stayed awake, but only when they were aware that they would be tested on this information.