Diffusion is the movement of a substance,
a. only through the lipid bilayer.
b. only in liquids.
c. only in air.
d. from an area of high concentrtion to an area of low concentration.

The correct answer of the statement is letter d.  Diffusion is the movement of a substance,from an area of high concentration to an area of low concentration. This makes other choices wrong. I hope I have helped and answered your question.

That is true! many fish species traveled to the u.s. because of it.