Diffusion refers to the force of attraction between the particles of the same substance the force of attraction between the particles of two different substances the random movement of one substance through another separation of one substance from another based on differences in density

The correct option is ' random movement of one substance through another'.

Explanation:

Diffusion is defined as movement of the particles from area having higher concentration to the area having lower concentration. It is usually observed  in gases and liquids.

For example: Drop of ink in water

cock topography

the study of the surface of a large voluptuous cock.

look at that sorostitute right she's a cock topographer!

what classes are you taking this

cock topography!

i believe the answer is a.