The Dimensions of An $\alpha$ Helix from a Fibrous Protein Such as Keratin Differ Slightly

Multiple Choice

The dimensions of an $\alpha$ helix from a fibrous protein such as keratin differ slightly from an $\alpha$ helix from a globular protein. What is the reason for this difference in helical dimensions?

A) An $\alpha$ helix from a fibrous protein is left-handed, not right-handed.
B) An $\alpha$ helix from a fibrous protein contains mainly hydrophobic residues, elongating the helix.
C) An $\alpha$ helix from a fibrous protein contains mainly polar residues, elongating the helix.
D) An $\alpha$ helix from a fibrous protein forms a coiled-coil, distorting the helix.
E) An $\alpha$ helix from a fibrous protein contains mainly Gly residues for more efficient packing.