Which is the most abundant protein in the animal kingdom?

Feathers and silk commonly contain . . . . . . .

Milk protein is:

Identify the protein structures shown in the image.

Which of the following statement$(s)$ is/are true?
$(i)$ All amino acids contain one chiral centre.
$(ii)$ Some amino acids contain one, while some contain more chiral centres or even no chiral centre.
$(iii)$ All amino acids in proteins have $L$-configuration.
$(iv)$ All amino acids found in proteins have $1^{\circ}$ amino group.

What type of structure do fibrous proteins possess?