I believe the correct response is D. A single variable.
Answer:
B. Allows for specialized regions with specialized functions
Explanation:
Where the complete digestive system has different specialized regions to perform specialized functions, the gastrovascular cavity is the primary organ of digestion and circulation in two major animal phyla: the Cnidaria (including jellyfish and corals) and Platyhelminthes (flatworms).
Higher phosphates is typically associated with a large amount of organic material in a water supply. A large amount of organic material implies rapid growth, so higher phosphates is the only feasible choice.
