How can amino acids be use to maintain the blood pH?

See the explanation below. Thanks!

Explanation:

The structure of an amino acid allows it to act as both an acid and a base. An amino acid has this ability because at a certain value (different for each amino acid) nearly all the amino acid molecules exist as zwitter-ions. If acid is added to a solution containing the zwitter-ion, the carboxylate group captures a hydrogen () ion, and the amino acid becomes positively charged. If base is added, ion removal of the ion from the amino group of the zwitter-ion produces a negatively charged amino acid. In both circumstances, the amino acid acts to maintain the pH of the system—that is, to remove the added acid or base from solution.

i'm thinking (a) to keep sand in place; ////////////

explanation: a sand fence or sandbreak, like a snow fence, is used to force windblown, drifting sand to accumulate in a desired place. sand fences are employed to control erosion, sand dune stabilization, keep sand off roadways, and to recruit new material in desert areas.