What causes dust particles and tiny grains of soot to move with Brownian motion?

a. Flowing currents
b. Collisions with transparent microorganisms
c. The element fire
d. Collisions with invisible molecules

this is poiselle's equation from fluid mechanic in physics. mech eng

igneous rocks also form where plates converge. the subducting plate melts as it sinks into the crust of the earth, and the melt rises into the overriding plate forming volcanoes. metamorphic rocks are formed mainly in the lithosphere, wherever there is high pressure and high temperature. -woods