Concept:Heat is a form of energy, so its SI unit is the same as the SI unit of energy, which is the joule.Explanation:The SI system defines the joule as the unit for all forms of energy, including heat. One joule equals the work done when a force of one newton moves an object one meter. Other units like calorie and erg also measure heat or energy, but they are not SI units. A calorie is the heat needed to raise 1 g of water by 1∘C. An erg is a smaller unit in the CGS system (1 erg=10−7 J). A watt measures power, not heat; it equals one joule per second. Thus, among the given options, only joule is the correct SI unit of heat.Answer:Option A: joule