Brownian motion is A. random movement of particles suspended in a fluid
B. movement of particles from an area of high concentration to low concentration
C. movement of particles from an area of low concentration to high concentration
D. random movement of smaller particles

A.

Explanation:

Brownian motion is the random motion of a particle as a result of collisions with surrounding gaseous molecules. Diffusiophoresis is the movement of a group of particles induced by a concentration gradient. This movement always flows from areas of high concentration to areas of low concentration.

Example:  The movement of pollen grains on still water. Motion of dust motes in a room (though largely influenced by air currents).