The correct answer is: a. water.

Why water is the answer

  • Water is classified as an essential nutrient because the body cannot survive without it and it is needed in larger amounts than any other nutrient.
  • It is involved in virtually every body function: transporting nutrients and oxygen, regulating temperature, removing waste, lubricating joints, and supporting cellular chemical reactions.

What about the other options?

  • Fats : Important macronutrient for energy, hormone production, and cell membranes, but not literally vital for every function.
  • Proteins : Crucial for structure, enzymes, hormones, and repair, yet many body functions depend more directly on water.
  • Carbohydrates : Main energy source but not required for every body function, and the body can produce glucose from other substrates if needed.

So in the context of the question “vital for every function of the body,” water is the best choice.

Information gathered from public forums or data available on the internet and portrayed here.