Which of the Following Statements Concerning Sleep-Assisted Learning Is True

Which of the following statements concerning sleep-assisted learning is true?

A) Sleep-assisted learning studies confirm that we can learn languages while we sleep.
B) Sleep-assisted learning tapes work because we actively process information while we sleep.
C) Sleep-assisted learning tapes work because we are likely not asleep when we listen to the tapes.
D) Most evidence from studies on sleep-assisted learning suggests that it is an effective learning strategy.