The primary sources of energy and comprise a significant part of a diet..They provide 4kcal of energy per gram.

The correct answer is **4) carbohydrates**.

Carbohydrates are the primary sources of energy in the diet and provide 4 kcal of energy per gram. This category includes sugars (like glucose) and starches, while fiber is a type of carbohydrate that is not digestible, hence it does not provide energy in the same way.