The correct answer is C. Thin film of oil in sea water.
An oil slick is a thin layer of oil that spreads over the surface of water. It can be caused by a variety of things, such as oil spills, natural seeps, and runoff from roads and parking lots. Oil slicks can have a devastating impact on marine life, as they can coat birds and other animals, making it difficult for them to breathe, swim, and find food. They can also kill plants and other organisms in the water.
Option A is incorrect because boiled oil is not a thin film. It is a thick, viscous liquid.
Option B is incorrect because cooled oil is not a thin film. It is a solid or semi-solid.
Option D is incorrect because oil in deep sea is not a thin film. It is a large, concentrated pool of oil.