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
Cyclic GMP is the second messenger of: 
Select and explain. 
A. Growth Hormone, B. Follicle Stimulating Hormone (FSH), C. Insulin, D. Thyroxin
C: Insulin
Answer: C: Insulin 
Explanation: C i.e. Insulin