I believe that the best answer to this question is d. amino acids.
<span>A trait that improves the fitness of its bearer, compared with individuals without the trait.</span>
Neurons function to process and transmit information. In vertebrate animals, neurons are the core components of the brain, spinal cord, and peripheral nerves.
The evolution of molecular biology has made possible to establish a new classification of all organisms according to their DNA, and it's called phylogenetic classification.This classification groups living beings according to their kinship, established according to anatomical, physiological and behavioral criteria and especially genetic, based on the similarity of genes between species.
This made it possible to discover kinship ties between species of which there is no suspicion of any morphological link between them, something which the old classification (the traditional classification) was incapable of doing (and this proves the importance of the DNA and genes in organisms classification.
