Which Is Not a Characteristic of an α-Helix

Which is not a characteristic of an α-helix?

A) The N-H and C=O bonds point along the axis of the helix in opposite directions.
B) The R groups of the amino acids extend inward toward the core of the helix.
C) There are 3.6 amino acids in each turn of the helix.
D) The C=O group of one amino acid is hydrogen bonded to an N-H group four amino acid residues farther along the chain.