By the time children are five years old:
A. the typical 90-minute sleep cycles of alternating REM and NREM are established.
B. about 50 percent of sleep time is spent in REM sleep and 50 percent is spent in quiet sleep that is very similar to NREM stages 1 and 2.
C. their sleep pattern is characterized by 60-minute sleep cycles, producing up to 13 cycles per day.
D. they will begin to experience their first dreams and nightmares.