Which Statement Does NOT Describe a Process by Which the Specificity

Which statement does NOT describe a process by which the specificity of aquaporins is ensured?

A) The channel contains a negatively charged Asp residue to scavenge protons and H₃O⁺.
B) The diameter of the channel narrows to 2.8 Å.
C) There are carbonyl backbone residues in the channel that hydrogen bond with water.
D) Arg and His residues in the channel repel protons and H₃O⁺.
E) Electric dipoles of short $\alpha$ helices repel protons and H₃O⁺.