There are six barrels of oil in the warehouse, each containing rapeseed oil, cottonseed oil and one barrel of tung oil. Each barrel is marked as containing 16 kg, 23 kg, 19 kg, 21 kg, 13 kg, and 15 kg of oil, but I don’t know which barrel it is What kind of oil is it containing? I only know that the weight of cottonseed oil is twice that of rapeseed oil. Please use calculations to distinguish the barrels containing tung oil.
仓库里有六桶油，分别盛有菜籽油、棉籽油和一桶桐油，各桶分别标明盛油16千克、23千克、19千克、21千克、13千克、15千克，可是不知哪一桶盛的是什么油，只知棉籽油的重量是菜籽油的2倍，请你通过计算把盛桐油的桶区别出来．
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