[Visitor (112.0.*.*)]answers [Chinese ] | Time :2022-05-18 | Common stains are made up of carbohydrates, fats, proteins, organic polymer compounds, or other types of organic compounds. Stains are a kind of dirt, mainly derived from the secretions and excrement of human skin, dust in nature and substances in animals and plants, minerals, or industrial raw materials, chemicals, etc. |
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