This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Cardiovascular system, Subject name: Physiology
True about troponin: 
Select and explain. 
A. Has 3 sub units, B. Troponin c binds to calcium, C. Troponin I binds actin and tropomyosine, D. All
D: All
Answer: D: All 
Explanation: Troponin is a complex protein: It has C,I,T sub units C binds to calcium Ref: Guyton and Hall textbook of medical physiology 12th edition, page number 89