<span>The circulatory system is vital in the exchange of oxygen with the cells in the animal's body because there is no living creature that can survive without oxygen, it keeps the body active.
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the correct answer is the first one. density = mass / volume.
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Answer:
To help organize data and record information
Biome, though some might say ecosystem instead. Biomes are very large ecosystems that cover broad areas.<span>If they specify "one" reef, then they are probably looking for "ecosystem"</span>