The most commonly used solvent in oil paints is turpentine. It is a clear, colorless liquid that is obtained from the resin of pine trees. Turpentine is used to thin oil paints, clean brushes, and remove dried paint. It is also used as a solvent in other products, such as varnishes and stains.
Petroleum is a liquid that is found in the earth. It is a mixture of hydrocarbons, which are compounds that are made up of hydrogen and carbon atoms. Petroleum is used to make gasoline, diesel fuel, and other products. It is not commonly used as a solvent in oil paints.
Spirit is a general term for a type of alcohol. There are many different types of spirit, but the most common type used in oil paints is mineral spirits. Mineral spirits is a clear, colorless liquid that is obtained from petroleum. It is used to thin oil paints, clean brushes, and remove dried paint.
Coal tar is a thick, black liquid that is obtained from coal. It is a mixture of many different compounds, including hydrocarbons, phenols, and naphthalene. Coal tar is not commonly used as a solvent in oil paints.
Therefore, the correct answer to the question is D. Turpentine.