Step-by-step explanation:
The teacher is most likely talking about the fractional distillation process.
Fractional distillation: It is a separation technique used to separate different components of the given mixture on the basis of their difference in boiling points of the different components. The component with lowest boiling point will get separate out first from the mixture and the vapors formed from boiling are condensed in a separate container.
So, when the fractional distillation of mixture of oils and fuels is carried out gasoline will separate out first due to lower boiling temperature and then kerosene followed by diesel and others (fuels and oils).