Research Has Shown That People Who Sleep 9 or More

Research has shown that people who sleep 9 or more hours per night spend a lot of that time in REM sleep, while those who sleep less than 6 hours get less REM sleep. This implies that

A) the body needs a certain minimum amount of REM sleep.
B) the body needs a certain minimum amount of non-REM sleep.
C) REM sleep does not serve an important function.
D) elderly adults get more REM sleep than adolescents.