Which statement best describes a cause and its effect that occurs during the process of muscle contraction?

Muscle contraction can be explained by sliding filament theory.  

1. Activation of muscles: the motor nerve generates an impulse to transfer signals from neurons to neuromuscular junction. This stimulates sarcoplasmic reticulum to release calcium into the muscle cells.

2.Contraction of muscles:  calcium in the muscle cells binds with troponin causes actin and myosin to bind. Actin and myosin in the muscle binds and contract by utilizing ATP as a source of energy.