Answer: D.by breaking chemical bonds
Step-by-step explanation:
The human beings are complex organisms which obtains energy by breaking the chemical bonds present in the food. The food we eat is composed of complex molecules of carbohydrates, fats and proteins which are digested by the fluids present in the stomach. The chemical bonds present between the molecules and atoms are broken during digestion process into simple substances which can be digested and absorbed by the body easily to obtain energy.