Which of the following amino acids contains sulphur?

What is the number of $-COOH$,$-NH_2$,$-H$,and $-R$ groups respectively in the structure of an amino acid?

What is a protein formed by different amino acids called?

Amino acids that are not synthesized in the body are called ...... .

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

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