Assertion: composition | /r/MadeOf | many trace elements
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Source sentences:
text: Although the composition of petroleum will contain many trace elements the key compounds are carbon (93% – 97%), hydrogen (10% - 14%), nitrogen (0.1% - 2%), oxygen (01.% - 1.5%) and sulphur (0.5% - 6%) with a few trace metals making up a very small percentage of the petroleum composition.