This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: A.N.S., Subject name: Pharmacology
Which of the following is fastest acting receptor? 
Select and explain. 
A. Beta1, B. M2, C. GABAa, D. Estrogen receptor
C: GABAa
Answer: C: GABAa 
Explanation: Ans. C. GABAaa. Ligand gated ion channels are the fastest acting receptors,b. Out of the options, the only ion channel receptor is GABAa.