The amino acid sequences below are found in an a-helix in the proteins below, as described. Match the protein to the helix. Only one of the sequences is not found as an a-helix at pH 7.

A: Val-Val-Ala-Gly-Val-Ala-Leu-Ala-Leu-Ala                    a. ____  at the surface of a water-soluble protein

B: Ala-Leu-Glu-Leu-Phe-Arg-Ile-Val-Met-Gln                    b. ____  a single helix that spans a biomembrane

C: Ser-Lys-Asn-Glu-Thr-Gln-His-Gly-Ser-Arg                    c. ____  a helix completely surrounding by water

D: Val-Glu-Asp-Pro-Asp-Gly-His-Lys-Pro-Arg                    d. ____  this sequence cannot be an a-helix