Concept:Fractional distillation separates petroleum fractions by boiling point differences.Explanation:In fractional distillation of petroleum, the crude oil is first heated until it evaporates.The vapours rise up the fractionating column.As the vapours cool, they condense at different heights based on their boiling points.So the main changes occurring are continuous evaporation and condensation.Diffusion and sublimation are not involved in this separation process.Answer:D. Evaporation and condensation