Which one of the following choices is not one of the main processes that allow nutrients to be absorbed from the GI tract into circulation?

A. Passive diffusion

B. Active diffusion

C. Facilitated diffusion

D. Active transport

The choice that doesn't reflect a main process which allows nutrients to be absorbed from the GI tract into circulation is active diffusion among these possible answers. So your answer would be B - active difusion.

The main reason for this is that all of the other ones are implicated and play active roles in the process of nutrient absorption from the GI tract into circulation.