Karl is 82 years old and has a grandson who is 24 years old. Neither of them has a sleep disorder. If they are typical of people their age, then at night during sleep, we most likely would find that Karl spends ___________ total time asleep per night than his grandson, and that this difference is mainly due to the fact that Karl spends ______________ than his grandson.
a. more; more time in Delta sleep
b. less; less time in Delta sleep
c. more; more time in REM sleep
d. less; less time in REM sleep