Answer:
a. Coelom
Explanation:
The coelom is the body cavity contain coelomic fluid. The organisms have a true coelom called the coelomate animals. Coelom gives space and provides protection to the internal organs. The coelom is present between the mesoderm and alimentary canal of the organisms. The invertebrates such as annelids, arthropods, helminths, echinoderms, and vertebrates have a true coelom.
