For a normal person, about how long does a cycle of sleep (from stage 1 to stage 4 and back again) last?
a. 10 minutes
b. 90 minutes
c. 4 hours
d. 7 hours
Question 2
After entering stage 4 for the first time each evening, the sleeper typically ____.
a. returns immediately to stage 1
b. enters REM
c. cycles back through stages 3 and 2
d. wakes up