Which system of grouping is in figure 18-2, a or b provides information about the evolution of the three animals

B

Explanation:

You have three stages for analyzing.

You start at B with a tiny free-swimming larva.

Some of those larvas start making segmentation. It is an evolutionary trait.

This divide what we today know as gastropods and those animals that continue with evolution.

Those segmentation larvas also evolve with a molten external skeleton which made them all crustaceans as we know them today.

Crab and barnacle are differentiation into the crustaceans.

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.