$7.$These terms: $-\frac{\text{d}\text{e}\text{l}\text{p}}{\text{d}\text{e}\text{l}\text{y}}+g_y+(\frac{de{l}^{2}v}{del{x}^2}+\frac{de{l}^{2}v}{del{y}^2}+\frac{de{l}^{2}v}{del{z}^2})$ in the Navier$-$Stokes equations physically represents what?

a$.$ Advective acceleration in the $y-$direction

b$.$ Viscous forces in the x$-$direction

c$.$ The sum of forces in the $x-$direction

d$.$ The sum of forces in the $y-$direction