This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: General physiology, Subject name: Physiology
Most distinguishing feature between skeletal muscle and smooth muscle 
Select and explain. 
A. Troponin, B. Tropomyosin, C. Myosin, D. Actin
A: Troponin
Answer: A: Troponin 
Explanation: Troponin is the calcium binding protein in the Skeletal muscle. In smooth muscle, calmodulin is the calcium binding protein. (REF: TEXTBOOK OF MEDICAL PHYSIOLOGY GEETHA N 2 EDITION, PAGE NO - 40,59)