Why Is REM Sleep Sometimes Referred to as Paradoxical Sleep

Why is REM sleep sometimes referred to as paradoxical sleep?

A) Brain waves are very slow, even if a person is dreaming about activity.
B) Body muscles are relaxed and immobilized, but the brain is active.
C) Sleepwalking may occur, but memory is not active enough to recall it.
D) Eyes are still, but people feel as if they are watching events in a dream.