Answer: The "pair of organisms that are in the same genus" (have more in common than the) "pair of organisms that are in the same phylum but not the same class".
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The reason is that the the "genus" is a more specialized sub-classification; and those pair of organisms in the same "genus" are, by definition /classification; already in the same phylum, same class, and same order, and same family, (and the phylum, class, order, and family all come before the "genus").
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