A normal healthy cell is bathed in a normal extracellular saline.  The plasma membrane of the cell contains voltage-gated sodium channels, sodium-glucose co-transporters, and sodium-potassium ATPase pumps. 

Via which of these spanning proteins is the net flux of sodium ions from a region of high concentration of sodium to a region of low concentration of sodium?  The movement of sodium ions via

A. an open voltage-gated sodium channel.

B. the sodium-glucose secondary active cotransporter.

C. the sodium-potassium ATPase primary active transport pump.