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
True about second messengers ? 
Select and explain. 
A. Act on intracellular receptors, B. Mediate response of extracellular hormones and neurotransmitter, C. Mediate response of intracellular hormones, D. Act by stimulation of transcription
B: Mediate response of extracellular hormones and neurotransmitter
Answer: B: Mediate response of extracellular hormones and neurotransmitter 
Explanation: Ans. is 'b' i.e., Mediate response of extracellular hormones and neurotransmitter