Answer:
C. Protect them from predators because their calcium carbonate exterior allows them to withstand an attack from their predators in their specific environment.
Explanation:
They build layers to protect themselves from predators. Plus, I've seen this question and got it right.
Atoms are indivisible spheres-Dalton model
John Dalton was the first to propose a theory to describe matter. As per Dalton's model, all matter is composed of atoms which resemble tiny 'ball-like' structures that are indivisible.
X - (1/2)
I'm pretty sure that's the answer
