What does 'Fire', 'Water' and 'Air' have in common?
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Actually fire is not a substance its just a chemical reaction i.e oxidation and which evolves heat.
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They're all part of the Earth, and All of the signs have the quality of one of the four elements. These are called the triplicates because they are a a group of three signs. For example, Aries, Leo and Sagittarius are a group of three fire signs.
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Oxygene