Sea stars, sea urchins, sand dollars, and brittle stars are all members of the same group.
what is the common name of the group to which they all belong?
1 annelids 2echinoderms 3arthropods 4cnidarians

The answer is Echinoderms

Explanation: The skin of most species is covered by spines, “warts,” or other projections.

when atoms of different types of elements join together, they make molecules called compounds. water consists of compound molecules made up of 2 hydrogen atoms and 1 oxygen atom. this is why it's called h2o. water will always have 2 times the number of hydrogen atoms as oxygen atoms.