How can the mass transfer kc and ultrafiltration solvent flux be increased?

Question

Select one:

a. Another stream of fluid can flow adjacent to the membrane to accumulate solute at the membrane surface

b. Another stream of fluid can flow perpendicular to the membrane to accumulate solute at the membrane surface

c. Another stream of fluid can flow through the membrane to transport away part of the polarised solute layer

d. Another stream of fluid can flow perpendicular to the membrane to transport away part of the polarised solute layer

e. Another stream of fluid can flow adjacent to the membrane to transport away part of the polarised solute layer.

I'm pretty sure the answer is either c or d, hope someone can clarify.Thanks.