Which one of the following statements about muscle contraction is true?
A) The actin heads move and pull on themyosin fibers during muscle contraction.
B) Muscle contraction causes sarcomeresto lengthen.
C) The lengths of thick and thinfilaments stay about the same during musclecontraction.
D) Thin filaments are primarily made ofmyosin.
E) Calcium provides the energy for musclecontraction.