Because oil is black, brown and red in color.

You should know that the second sentence of the riddle is petroleum, because the color of petroleum is black and brownish red, corresponding to "embracing ten thousand red", and the ancient name for petroleum is "black water", and "petroleum" is the Chinese name for the water in the Northern Song Dynasty, which was used by scientists to describe their work. The Chinese name "oil" was first named by the Northern Song Dynasty scientist Shen Kuo.

It should be noted that the second sentence of the "water in the water black water", because the nature of the oil varies depending on the origin, the viscosity range is very wide, the freezing point varies greatly, the boiling point range of room temperature to more than 500 degrees Celsius, can be dissolved in a variety of organic solvents, insoluble in water, but can be with the water to form an emulsion, which is why it is called "water in water black water".

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It is important to know that as early as the 10th century BCE before ancient Egypt, Ancient Babylon and India and other ancient civilizations have collected natural asphalt, used in construction, antiseptic, adhesive, decorative, pharmaceuticals, the ancient Egyptians can even estimate the amount of oil oozing out of the oil seedlings.

The formation mechanism of petroleum has been the subject of much debate in the scientific community. There are two main streams, one is the biological change to oil, and the other is the petrochemical change to oil. The mainstream Western doctrine that oil is buried in the ground billions of years ago in the biological evolution of high temperature and high pressure environment, belonging to the use of a little less, non-renewable resources.