During which stage of sleep, also known as delta sleep, would a person have slow breathing and be difficult to wake.
A.
between stages 1 and 2 of non–rapid-eye-movement sleep
B.
in stage 4 of non–rapid-eye-movement sleep
C.
near the end of stage 3 of rapid-eye-movement sleep
D.
in stage 3 of non–rapid-eye-movement sleep