OPT: (a). characteristics; (b). centralized nervous system; (c). permineralization; (d). the body's largest organ; (e). biological diversity; (f). that material's properties; (g). aerobic capacity; (h). organic matter;

Fact 1: Echinoderms lack a centralized nervous system. Fact 2: Another group of echinoderms are the echinoids. Given the two facts above, what do echinoids lack?
Answer:
(b).