In diffusion, movement of particles across a membrane is driven by differences in

a. shape.
b. force.
c. size.
d. concentration.

Concentration. Diffusion is the net movement of molecules from a region of high concentration to a region of low concentration.

Apicture would .

Ibelieve the answer is relative humidity  because it makes more sense that way. solar flares usually occur in space it doesn't affect the earth, well it could but it wont make a significant damage.  latitude is land it doesnt do anything. prevailing winds, i dont know the correct meaning for this but i doubt that affects the land so it has to be relative humidity.