Researchers Who Have Looked at Changes with Age in Total

Researchers who have looked at changes with age in total amounts of daily REM sleep and NREM sleep have found that

A) the amount of REM sleep increases considerably over the years.
B) NREM diminishes more sharply than REM sleep over the years.
C) the amount of REM sleep decreases considerably over the years.
D) REM sleep remains fairly constant over the years, but NREM increases slightly.