This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Misc., Subject name: Physiology
[{'content': 'Which one of the following is absent in smooth muscles? \nSelect and explain. \nA. Actin, B. Myosin, C. Troponin, D. Myosin adenine triphosphatase', 'role': 'user'}, {'content': 'Answer: C \nExplanation: (C) Troponin> Smooth muscle have no troponin or tropomyosin, but they have actin and myosin.> They have no sarcoplasmic reticulum, No T-tubule.> No Z lines. The contraction is stimulated by extracellular ca+.> Latching - is the characteristic of smooth muscle. Even after the dephosphorylation of myosin, the cross bridges continue to attach in the same position for some time. There is no fixed tension relationship.', 'role': 'assistant'}]