The Most Common Motif Found in Membrane Spanning Proteins Is $\alpha$

Multiple Choice

The most common motif found in membrane spanning proteins is

A) $\alpha$ helices of nonpolar amino acids that pass through the membrane.
B) $\alpha$ helices of charged amino acids that form channels via extensive hydrogen bonding.
C) a triple helix of $\alpha$ helices.
D) a helix-turn-helix arrangement of the peptide strands.
E) None of the answers is correct.