Which Statement Best Describes the Pattern of Sleeping and Waking

Which statement best describes the pattern of sleeping and waking in relation to body temperature

A)  We fall asleep as temperature becomes stable and wake as it starts to fluctuate. 
B)  We fall asleep as temperature begins to rise and wake as it drops. 
C)  We fall asleep as temperature begins to drop and wake as it goes up. 
D)  We fall asleep as temperature starts to fluctuate and wake as it becomes stable.