Answer:
A. Solubility and density.
Step-by-step explanation:
The oil is insoluble in water, so the liquids form two layers.
The oil is less dense than water, so it floats on top of the water, where you can skim it off.
B, C, and D are wrong. If you are skimming off the oil, you aren’t using its magnetism, boiling point, particle size, or colour for the separation.