What does the human body require to function properly?

The human body requires fuel to function properly, which refers to the energy necessary for all bodily processes. This fuel primarily comes from macronutrients like carbohydrates, fats, and proteins that provide the energy needed for movement, growth, and maintaining bodily functions. Every cell in the body relies on this energy to perform its tasks, including metabolic reactions, muscle contractions, and even mental activities.

While vitamins, fiber, and micronutrients play important roles in supporting overall health, such as immune function, digestion, and cellular repair, they are not the primary source of energy. Instead, they complement the body's needs by promoting various biochemical pathways and ensuring that the body runs efficiently. However, without an adequate supply of fuel, the body would struggle to perform even basic functions, leading to fatigue and other health issues. Hence, the correct choice highlights the fundamental requirement of energy for proper human body function.