[单选题]
Which is not a correct definition or equartuoo p9y(m/+tion for water *sigx,p;d/c yjr:im; potential?
A. The sum of the solute and pressure potential of a solvent
B. ψ$_w$ = ψ$_s$ + ψ$_p$
C. The direction that water will move through a semipermeable membrane
D. The potential energy of water per unit volume
