Which one of the following is the correct sequence of events that follows a threshold potential:

1. the membrane becomes depolarized
2. sodium channels open and sodium ions diffuse inward
3. the membrane becomes repolarized
4. potassium channels open and potassium ions diffuse outward while sodium is actively transported out of the cell
.
A. 3,2,4,1

B. 2,1,4,3

C. 2,1,3,4

D. 1,2,4,3