Qìchē fángdòngyè de zhǔyào chéngfèn shì yǐ'èrchún.
The main ingredient of car antifreeze is ethylene glycol.
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乙 'two carbons' + 二 'two' + 醇 'alcohol': a two-carbon alcohol with two hydroxyl groups, which is exactly what ethylene glycol is. Add 聚 'poly-' and you get 聚乙二醇 (PEG), a different substance used in medicines and cosmetics.