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
Which receptor is responsible for monitoring the rate of muscle stretch? 
Select and explain. 
A. Nuclear bag intrafusal fibers, B. Nuclear chain, C. Golgi tendon organ, D. Pacinium corpuscles
A: Nuclear bag intrafusal fibers
Answer: A: Nuclear bag intrafusal fibers 
Explanation: None