Which of the following statements is true of stage 4 sleep?

A) It produces low-amplitude brain waves.
B) It is the lightest stage of sleep.
C) During stage 4 sleep, the delta waves produced by the brain slow to about 0.5 to 2 cycles per second.
D) During stage 4 sleep, the delta waves produced by the brain have a frequency of 8 to 13 cycles per second.

C