What variable(s) increased the rate of facilitated diffusion of glucose?

variables that help to increased the rate of diffusion are

1) concentration of glucose

2) by increasing the number of membrane carriers

Explanation:

variables that help to increased the rate of diffusion are

1) concentration of glucose - the rate of diffusion increased when molecules concentration outside the cell is more than internal concentration. It is all part of the concentration gradient. Higher the concentration gradient higher will be the rate of  diffusion

2) by increasing the number of membrane carriers - the rate of diffusion increased by increasing concentration of solute in the cell which is increase by carrier proteins.

the answer is d.index