Which of the Following Is True of Human Sleep Cycles

Multiple Choice

Which of the following is true of human sleep cycles?

A) Sleep cycles are random across the night.
B) Subjects first enter REM sleep and then transition to non-REM sleep.
C) As the night goes on, the relative length of REM sleep increases in each successive cycle.
D) Stage 3 of slow-wave sleep mostly occurs in the early morning hours.
E) Each non-REM/REM cycle lasts about 45 minutes.