Which of These Statements Describes Contraction in Skeletal and Smooth

Which of these statements describes contraction in skeletal and smooth muscle

A) In skeletal muscle, calcium ion mediates changes in thin filaments that lead to cross-bridge activity; in smooth muscle, calcium ion mediates changes in thick filaments that lead to cross-bridge activity.
B) In skeletal muscle, troponin and tropomyosin are regulatory proteins; in smooth muscle, troponin is the only regulatory protein on thick filaments.
C) In skeletal muscle, calcium ion binds to troponin; in smooth muscle, calcium ion binds to calmodulin.
D) In skeletal muscle, calcium ion binds to calmodulin; in smooth muscle, calcium ion binds to troponin.