A powder derived from the North American Echinacea flower, which has been effective in preventing colds, is grown by many small farmers out West.
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AA powder derived from the North American Echinacea flower, which has been effective in preventing colds,
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BA derivative, which has been effective in preventing colds, of North American Echinea flower,
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CNorth American Echinacea flower derivative, which has been effective in preventing colds
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DThe North American Echinacea flower has a derivative which has been effective in preventing colds, that
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EThe North American Echinacea flower, a derivative of which has been effective in preventing colds,
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正确答案: E