Which one of the following is an amino acid?

Sulphur $(S)$ containing amino acids from the following are:
$(a)$ isoleucine
$(b)$ cysteine
$(c)$ lysine
$(d)$ methionine
$(e)$ glutamic acid

Assertion $(A)$: An optically active amino acid can exist in three forms depending on the $pH$ of the solution.
Reason $(R)$: Amino acids contain both acidic and basic groups; they exist as a zwitterion in aqueous medium,anionic form in basic medium,and cationic form in acidic medium.

The correct zwitter ion structure of glycine is

Proteins can be used:

The condensation polymer among the following is