Which describes step three of a muscle contraction?

The answer is step 3. Nerve impulse on a muscle cell induces release of calcium ions

Steps of a muscle contraction are:
1. Nerve impulse travels down the axon and causes a release of acetylcholine.
2. Acetylcholine binds to the receptor of a muscle cell.
3. Nerve impulse on a muscle cell induces a release of calcium ions.
4. Calcium ions induce exposing of myosin to actin.
5. Sliding of actin filaments past myosin filaments.
6. The muscle contract.

The answr is c. Facilitated diffusion