Which of the following is a true statement of diffusion? a.) diffusion is only important for animal cells. b.)diffusion require energy input from the cell. c.) only water can diffuse across a cell membrane d.) molecules move from areas of high concentration to areas of low concentration.

I believe the answer is D :) 

A is wrong because all cells can undergo diffusion
B is wrong because diffusion does NOT need energy input from the cell
C is wrong because that is only true for osmosis 
 

the correct option is D ..
because diffusion is the movement of molecules whether gas or liquid from area of high concentration to that of low concentration .. 
for example : if you spray perfume at one corner of the room soon you will be able to smell it at other corner .. this movement of molecules from one corner( high concentration)  to other (low concentration) is due to diffusion ..

The answer is a if u read the definition it makes sense