<span>Transfer of materials into a cell against a concentration gradient from low to high concentration requires active transport because you need energy for it to happen since its going againist the concentration gradient.
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The nervous system is referred to as a communication system because it carries messages to and from all parts of the body.
Well, right away I know that it is some sort of mutualistic relationship. Since this is not an option here, my best guesses are either <em>B or C.</em>
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Please let me know if I was right :)
