Answer: Carbohydrates
Step-by-step explanation:
If many sources of energy is present then the body will first utilize carbohydrates then once all the carbohydrates of the body is utilized then the body will move to another sources such as fats and proteins.
The reason being that the oxidation of carbohydrates requires less energy as compared to fat and proteins.
The primary source of energy inside the body is carbohydrates so this will be used by the body firstly.