<em>Animals are a group of organism that are multi-cellular in nature and whose cells lack cell walls.</em>
From the choices above, algae are plants whose cells have rigid cell walls, fungus cells also have cell walls, protozoans are unicellular while bacterium also have protective cell walls/capsule.
The only option that is an animal without cell wall is helminth.
Natural selection is when the organisms that have the better adaptation so they survive. In this case, the green was the better adaptation so they lived.
