This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Physiology
What is the effect of sleep on cardiac output? 
Select and explain. 
A. Cardiac output increases, B. Cardiac output decreases, C. Cardiac output remains same, D. Can't say
C: Cardiac output remains same
Answer: C: Cardiac output remains same 
Explanation: No change in Cardiac output occurs during sleep.