Which of the following is responsible for the rapid depolarisation phase of the myocardial action potential.. Rapid sodium influx

Which of the following is responsible for the rapid depolarisation phase of the myocardial action potential?
A.A Rapid sodium influx***
B.A Slow sodium efflux
C.A Slow efflux of calcium
D.A Efflux of potassium
E.A Rapid calcium influx.