Once an SA Nodal Cell Reaches Threshold, the Depolarization Phase

Once an SA nodal cell reaches threshold, the depolarization phase occurs during which

A) potassium comes in through fast voltage-gated channels.
B) calcium comes in through fast voltage-gated channels.
C) potassium moves out through fast voltage-gated channels.
D) sodium moves out through slow voltage-gated channels.
E) calcium moves out through slow voltage-gated channels.