Which of the following is a storage protein?

The correct option is D Glutelin
Glutelin is a storage protein found in certain seeds of cereals like wheat, maize, etc. It is a component of the protein gluten that gives dough it’s elasticity.

Collagen and keratin are structural proteins.
Collagen is a structural protein present mainly in the extracellular matrix. It is the most abundant protein in the animal world. It is a fibrous protein typically long, elastic and has a helical structure.
Keratins are simple fibrous proteins present in eukaryotes. They can occur as helical ⍺-keratin or 𝛽-keratin. In vertebrates, almost the entire dry weight of hair, wool, feathers, nails, horns, hooves and the majority of the outer skin layer occur as ⍺-keratin. It serves important protective and structural functions.

Starch is not a protein but a storage polysaccharide found in plants.