Beginning with depolarization at the neuromuscular junction, describe the normal sequence of events which lead to muscle contraction

Depolarizing urges release Ach from the nerve ending, which diffuses across the neuromuscular junction. At the muscle membrane, Ach attaches to receptor sites. As sodium channels begin to open, ions cross the membrane. Also, the action potentials are then elicited. 

it is either c or d and i know for sure it is not a or b

option c is the correct answer.