Monosaccharides are the basic units of carbohydrates. They are the simplest form of carbohydrates and cannot be further hydrolyzed into smaller units. Examples of monosaccharides include glucose, fructose, and galactose. Disaccharides, on the other hand, are formed by the condensation of two monosaccharide units, while polysaccharides are formed by the condensation of many monosaccharide units. Macronutrients, on the other hand, refer to the essential nutrients needed in large amounts by the body, including carbohydrates, proteins, and fats. Therefore, the correct answer is monosaccharides.