What Prevents Proton Translocation Through Aquaporins

What prevents proton translocation through aquaporins?

A) Asp and Glu residues bind to protons to prevent their translocation.
B) Carbonyl groups in the selectivity filter interact with water molecules.
C) Two side chain amide groups act as hydrogen bond donors to a single water molecule.
D) All of the answers are correct.
E) None of the answers is correct.