In excitation-contraction coupling,
A. myosin heads bind to exposed active sites on actin.
B. ATP binds to actin myofilaments.
C. Ca2+ must bind with myosin to expose active sites on actin.
D. movement of the troponin-tropomyosin complex causes actin myofilaments to slide.
E. cross-bridges form between myosin heads and Ca2+.
Answer: A
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