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
cGMP is second messenger for which of the following harmone 
Select and explain. 
A. Atrial  natriuretic factor, B. Nitric acid, C. Both of the above, D. None of the above
C: Both of the above
Answer: C: Both of the above 
Explanation: Atrial  natriuretic factor (ANF) and Nitric acid (NO) user cGMP as second messenger.