Corals is/are
A. The tiny animals that live in shells in the sea.
B. A special variety of fish which live in shells
C. A particular type of shell found near some of the sea coasts
D. The remains of tiny sea animals resembling shells

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Hint: Corals are a member of the phylum Cnidaria or Coelenterata. The word Cnidaria is made up of two words, ‘Cnida’ meaning sting, and ‘Aria’ meaning bearing. Moreover, the phylum Cnidaria consists of animals with the stinging cells or the nematoblast cells, or the Cnidoblast cells.

Complete answer: Corals belong to the class Anthozoa of the phylum Cnidaria. These organisms are exclusively marine. They are an exception to the phylum Cnidaria in terms of the skeleton. All the members of the phylum Cnidaria do not have any skeleton; however, corals have a skeleton formed by the deposition of the calcium carbonate around them. Due to this, they appear as tiny animals living inside the shells. Corals live in compact colonies of identical polyps. They are the important reef builders. The great barrier reef of Australia is all the corals. Corals grow by asexual reproduction. They catch their prey with the help of the tentacles on their head and the stinging cells. Corals are found in a symbiotic relationship with dinoflagellates, which provide them with the energy and the nutrients. Thus, based on the above information we can conclude that the corals are tiny animals that live in shells in the sea.
Hence, the correct answer is option A.

Note: The phylum Cnidaria is divided into three classes based on metagenesis. The metagenesis is the alternation of the generation. The cnidarians change between two forms during their lifecycle. These two forms are the free polyp stage and the floating medusa stage. The three classes are Hydrozoa,
Scyphozoa and Anthozoa.