Which process must occur for a muscle to be able to relax? a. the concentration of calcium in the myofibril must decrease. b. the amount of atp in the neuromuscular junction must increase. c. a nerve must initiate an action potential in the muscle fiber. d. myosin and actin must attach to each other.

The correct option is A. which is the concentration of calcium in the myofibril must decrease.

Explanation:Calcium allows the actin, myosin, and ATP to interact, causing cross bridge formation and muscle contraction. Muscle relaxation occurs when calcium is pumped back into the sarcoplasmic reticulum, away from the actin and myosin. When calcium moves in this way, the actin and myosin cannot interact, and the muscle relaxes.So according to above information all option are wrong except A option.

The most plausible answer is b, duration. the given amount of time is considered how long it last for.