Question

1. dead echinoderms are naturally recycled to make which product?

○ they are the main ingredient in toothpaste.
○ they are the main ingredient in limestone.
○ they are the main ingredient in livestock feed.
○ they are the main ingredient in collagen.

Explanation:

Echinoderms (like sea urchins, starfish) have skeletons made of calcium carbonate. When they die, their remains accumulate and over long geological times, compact and form limestone, which is primarily composed of calcium carbonate. Toothpaste uses synthetic or mined abrasives, livestock feed relies on plant/animal proteins, and collagen comes from animal connective tissue, not echinoderms.

Answer:

They are the main ingredient in limestone.