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: Pharmacology
Which of the following is not a hydrophobic secondary messenger? 
Select and explain. 
A. DAG, B. IP3, C. Phosphatidyl inositol, D. cAMP
D: cAMP
Answer: D: cAMP 
Explanation: None