If Polar Amino Acids Are Found in a Membrane Spanning $\alpha$

If polar amino acids are found in a membrane spanning $\alpha$ -helical region, they are most likely _____.

A) mutations
B) modified with nonpolar groups by prenylation, methylation and/or acylation
C) hydrogen-bonded to other polar amino acids to prevent interaction with the membrane lipids
D) hydrogen-bonded with hydroxyl groups of the membrane fatty acids
E) none of the above