Concept:Phosphorus is a major mineral that works with calcium to build and maintain strong bones and teeth.
Explanation:About 85% of the body's phosphorus is found in bones and teeth.
It is essential for mineralization, giving bones their strength and rigidity.
While phosphorus also helps maintain pH balance and is part of ATP (energy) for muscle and nerve function, these are not its primary roles.
Calcium plays a more direct role in regulating muscle contractions.
Sodium, potassium, and calcium are more directly involved in nerve impulse transmission.
Thus, the main function of phosphorus is the development of bones and teeth.
Answer:A. Development of bones and teeth