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
G protein coupled receptor ? 
Select and explain. 
A. NMDA receptor, B. Steroid, C. M2, D. Insulin receptors
C: M2
Answer: C: M2 
Explanation: Ans. is 'c' i.e., M2M2 muscarinic receptors are G-protein coupled receptors and act through cAMP.