Here's why:

* Hydrogen (H), Oxygen (O), Carbon (C), and Nitrogen (N) are the four main elements that make up all amino acids.

* Sulfur (S) is found in the amino acids cysteine and methionine.

Proteins are made up of long chains of amino acids linked together. These chains can fold and twist into complex three-dimensional shapes, allowing proteins to perform a vast array of functions in living organisms, including:

* Enzymes: Catalyzing biochemical reactions

* Structural components: Providing support and shape

* Hormones: Regulating bodily functions

* Antibodies: Defending against infections

* Transport proteins: Moving molecules across cell membranes

While proteins are the most prominent examples, other large molecules can also contain these elements:

* Nucleic acids (DNA and RNA) also contain hydrogen, oxygen, carbon, and nitrogen, but not sulfur.

* Carbohydrates contain hydrogen, oxygen, and carbon, but not nitrogen or sulfur.

* Lipids are diverse, but most contain hydrogen, oxygen, and carbon, and some contain small amounts of nitrogen or sulfur.

However, the combination of all five elements (hydrogen, oxygen, carbon, nitrogen, and sulfur) strongly points to proteins as the primary large molecules you're looking for.