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 one of the following is a regulatory protein of the muscle? 
Select and explain. 
A. Troponin, B. Myosin, C. Actin, D. Protein-C
A: Troponin
Answer: A: Troponin 
Explanation: None