Why can dna, rna, and proteins be used to compare only living organisms?

They only work in things that still function

All these are used to make the organism function thus are used for only the living.

Explanation:

DNA is found in every nucleus of an organism that is exactly same in all the cells and is true to all the life forms on earth and the synthesis of the RNA firm DNA is called as translation and formed into proteins and is made of amino acids and these proteins re essential for the development of the living organisms.

Ansradar; im guessing here; good luck : )