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The chemical composition of essential oil obtained by hydrodistillation of the fresh aerial parts of Mentha requienii Bentham ( Lamiaceae ) collected on the Gennargentu Mountains ( Sardinia , Italy ) has been investigated by gas chromatography and gas chromatography - mass spectrometry .
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Please list all entity words in the text that fit the category. Output format is "word1, word2". 
Option: Chemical 
Text: {0} 
Answer:
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