Advection is

a. Fluid's bulk motion

b. Transporting a substance by a fluid due to the fluid's bulk motion

c. Movement of fluid’s molecules

d. Movement of fluid from lower pressure place to higher pressure place

ANSWER: Transporting a substance by a fluid due to the fluid's bulk motion

Explanation:

Advection is a transport mechanism of a substance or conserved property by a fluid due to the fluid's bulk motion.

An example of advection is the transport of pollutants or silt in a river by bulk water flow downstream. Another commonly advected quantity is energy or enthalpy.

Advection is sometimes confused with the more encompassing process of convection.

Convection is the concerted, collective movement of groups or aggregates of molecules within fluids (e.g., liquids, gases) and rheids, through advection or through diffusion or as a combination of both of them.