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
CyAMP acts as a second messenger of: 
Select and explain. 
A. FSH, B. Growth hormone, C. Thyroxine, D. Insulin
A: FSH
Answer: A: FSH 
Explanation: A i.e. FSH