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
[{'content': 'The  site  where  myosin  heads  bind  to actin  in  skeletal  muscles  are  covered by: \nSelect and explain. \nA. Tropomyosin, B. Troponin, C. Calcium, D. None of the above', 'role': 'user'}, {'content': 'Answer: A \nExplanation: In\xa0the\xa0resting\xa0state,\xa0the\xa0tropomyosin molecules lie on top of the active sites of the\xa0actin strands, so that attraction cannot occur between the actin and myosin filaments to\xa0cause contraction.', 'role': 'assistant'}]