D. Both B & C.
Active transport and facilitated diffusion differ in the following ways:
1. Energy requirement: Active transport requires the input of energy, usually in the form of ATP (adenosine triphosphate), to move molecules across the cell membrane. On the other hand, facilitated diffusion does not require energy.
2. Concentration gradient: Active transport moves molecules against their concentration gradient. This means it can move molecules from an area of lower concentration to an area of higher concentration. Facilitated diffusion, however, moves molecules down their concentration gradient – from an area of higher concentration to an area of lower concentration.
In summary, active transport requires energy and can move molecules against their concentration gradient, while facilitated diffusion does not require energy and moves molecules down their concentration gradient. Therefore, the correct option is D.