The correct option is D Fractional distillation
If the difference between the boiling points of the mixture of miscible liquids is less than 25 ∘C, then fractional distillation is used to separate components of the mixture.
Crude oil which is drilled out from the depth of the Earth, is a mixture of miscible liquids (paraffin, diesel, fuel oil, etc.) and the difference in the boiling points of these components is less than 25 ∘C.
Hence, fractional distillation is the method used to obtain the different components (paraffin, diesel, fuel oil etc.) from crude oil.