Dusty and sand particles present in the air form a suspension because it is a heterogeneous mixture where solid particles are dispersed in a gas (air).

B. a dispersion: is a general term for any system in which particles of one material are distributed in a continuous phase of another. Suspension is a specific type of dispersion.

C. an emulsion: is a specific type of colloid where both the dispersed phase and the dispersion medium are liquids that are typically immiscible (do not mix). Eg milk.

D. a saturated solution: is a homogeneous mixture (a true solution) where the maximum amount of a solute has been dissolved in a solvent at a specific temperature. The particles are molecular in size and do not settle. Air with dust and sand is not a solution as the particles do not dissolve.

The correct answer is suspension - option A