Concept:Living organisms need complex energy-rich organic nutrients, and these are obtained from food.
Explanation:Food contains carbohydrates, fats, and proteins, which are complex organic compounds.
These compounds store chemical energy in their bonds.
During respiration, this energy is released to support life processes like growth, movement, and reproduction.
Water, air, and mineral salts are essential, but they are inorganic or simple substances.
They do not act as complex energy-rich organic matter.
Thus, among the given options, food is the only material that supplies such nutrients.
Answer:C. food