Here's why:

* Sulfur (S): A crucial component of amino acids (building blocks of proteins), vitamins (like biotin), and other essential molecules.

* Sodium (Na): Plays a vital role in nerve impulse transmission, muscle contraction, and maintaining fluid balance.

* Selenium (Se): A component of certain enzymes involved in antioxidant defense and thyroid hormone metabolism.

Strontium, while a naturally occurring element, has no known essential biological role in humans or most other organisms. In fact, high levels of strontium can be toxic.