Charlene Is 12, and Her Elderly Aunt Has Come for a Visit

Charlene is 12, and her elderly aunt has come for a visit. The aunt is using the spare bed in Charlene's room. Several times during the night, the aunt awakens briefly and then falls back to sleep. Charlene doesn't awaken at all during the night. This difference in sleep patterns can BEST be explained by research that shows

A) during adulthood, the proportion of REM sleep gradually increases.
B) during adulthood, the proportion of slow-wave sleep increases significantly.
C) the elderly are more affected by jet lag and shifts in their circadian rhythm.
D) during adulthood, the proportion of slow-wave sleep gradually declines.