Answer:
C. Both
Step-by-step explanation:
The movement of molecules from an area of high concentration to an area of low concentration is called Diffusion.
In simple difussion the movement of molecules is driven by a gradient in concentration in a solution or across a semipermeable membrane.
Unlike simple diffusion, in facilitated diffusion membranes incorporate specialized membrane proteins which help transport substances across the membrane, and also the direction of transport is always down a concentration gradient, from an area of high concentration to an area of low concentration.