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
Calcium ions triggers muscle contraction by binding to: 
Select and explain. 
A. Actin, B. Myosin, C. Troponin, D. Tropomyosin
C: Troponin
Answer: C: Troponin 
Explanation: None