Which protein is found in the greatest abundance in the animal kingdom?

Which of the following is an amino acid?

Which of the following bonds does not participate in the formation of the quaternary structure of proteins?

$A$: Tertiary structure of protein molecules makes them biologically active.
$R$: It is the native configuration of protein molecules maintained by multiple covalent bonds only.

The most widely accepted method for the classification of amino acids is based on:

Which one is the most abundant protein in the animal world?