Which of the following is NOT considered as a major driving force for water flow from the soil through the plant to the atmosphere?
选项：

A:Difference in water vapor concentration between leaf and air, responsible for the diffusion of water vapor from the leaf to the air.;
B:Difference in hydrostatic pressure, responsible for the bulk flow of water through xylem.;
C:Difference in water potential, responsible for the movement of water across the living cells in the roots.;
D:Elevation of the plant.