Which statements correctly explain the distribution of water on Earth? Check all that apply. One-fourth of Earth’s water is frozen water. One-fourth of Earth’s water is groundwater. Salty water makes up 97% of Earth’s water. Fresh water makes up 3% the Earth’s water. The atmosphere contains 3% of Earth’s water. Lakes and rivers contain 97% of Earth’s water.

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organisms that lack symmetry are called asymmetrical and belong to phylum porifera/sponges.

organisms with specialized stinging cells belong to phylum cnidaria. stinging cells are called cnidoblast cells.

cnidarians show two morphological forms : polyp (sessile) and medusa (mobile)

filter feeding is observed in porifera members.  

alternation of generation is observed in coelenterata or cnidaria. there is alternation of asexual polyp form and sexual medusoid form. it is also referred as metagenesis.

well, that's easy; the answer's c, "it reduces contamination of the water and substrate of the estuary."