Concept:A solid emulsion is an emulsion that exists in a solid or semi-solid state at room temperature.Explanation:An emulsion is formed when two immiscible liquids are mixed, such as oil and water.Butter is a water-in-oil emulsion that is solid or semi-solid at room temperature.Milk is a liquid emulsion, and cod-liver oil is simply an oil, not a solid emulsion.Therefore, butter is the correct example of a solid emulsion.Answer:A. Butter