The correct answer is C) 80°F (27°C). A combustible liquid is defined as any liquid having a flash point at or above 80°F (27°C) and below 200°F (93°C). This definition is established by the U.S. Coast Guard regulations for Captain's License examinations. Liquids with a flash point above 80°F are considered combustible, while those with a flash point below 80°F are classified as flammable liquids. The other answer choices are incorrect because 110°F (43°C) is too high, 40°F (4°C) is too low, and 150°F (66°C) is also too high to define the flash point threshold for a combustible liquid.