A tetanic contraction produces more force than a single twitch because: a. The levels of calcium in the sarcoplasm of the skeletal muscle stay higher for longer during a tetanic contraction. b. A maximum number of myosin cross bridges are interacting with the thin filaments during a tetanic contraction. c. The sarcoplasmic reticulum does not release calcium during a single twitch. d. The binding sites on the thin filaments that the myosin heads attach to stay exposed for longer during a tetanic contraction.