46. Which of the following best expresses the main idea of the passage?
(A) Ancient civilizations understood the true purpose of dreaming far better than modern neuroscientists do.
(B) Dreaming is a complex cognitive process that serves essential functions in memory, emotion, and survival.
(C) The reduction of activity in the prefrontal cortex is the sole reason why humans experience dreams.
(D) Threat simulation is the most widely accepted scientific explanation for why humans enter REM sleep.