The correct answer is d) oil.
When lipids are liquid at room temperature, they are typically referred to as oils. This is mainly due to the presence of unsaturated fats, which have one or more double bonds in their fatty acid chains. These double bonds create kinks in the structure, preventing the molecules from packing tightly together, which keeps them in a liquid state at room temperature. While unsaturated fat and polyunsaturated fat describe types of fatty acids, the general term for lipids found in a liquid state at room temperature is oil.