This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Nervous System, Subject name: Physiology
Circadian rhythm is controlled by: 
Select and explain. 
A. Suprachiasmatic nuclei, B. Hypothalamus, C. Thalamus, D. Pineal gland
A: Suprachiasmatic nuclei
Answer: A: Suprachiasmatic nuclei 
Explanation: A