Which characteristic do protozoans foraminiferans (phylum sarcodines) and coccolithophores (phylum haptophyta) have in common?

The other answer is correct, but more specifically:

D. They both develop calcium carbonate structures.

The addition of calcium carbonate makes exoskeletons harder/stronger.

The answer should be D because the skin. Has layers correct but there really thick and it makes bacteria and infections hard to pass through but at the same time we have already dead skin cells on us that either block out or destroy others layers that can’t infect the skin