Which statements about these carbohydrate derivatives are true?
a. n‑acetylneuraminic acid is a six‑carbon acidic sugar derivative.
b. n‑acetylneuraminic acid is a component of some cell membrane glycoproteins.
c. n‑acetylmuramic acid contains an n‑glycosidic bond.
d. n‑acetylneuraminic acid is a component of bacterial membranes, but not animal membranes.
e. n‑acetylmuramic acid is a component of the repeating peptidoglycan unit of bacterial cell walls.