Which statement is the best description of the sleep pattern for a normal adult?
a. sleep problems decrease in middle aged adults.
b. most of the sleep cycle is made up of rapid eye movement (rem) sleep.
c. an adult has four to six sleep cycles, each with non-rapid eye movement (nrem) sleep and rapid eye movement (rem) sleep, during a normal night's sleep.
d. a middle-aged adult requires less sleep than an elderly adult.