Audi has announced a process by which hydrocarbon liquids can be made from water and carbon dioxide. Some readers have responded to this news by saying, "I knew it! I just knew one day they'd find a way to run cars on water!" But then even the most credulous among us feels that tickle of skepticism. Wait a minute. Aren't carbon dioxide and water the products of hydrocarbon combustion? The carbon combines (burns) with oxygen from the air to make carbon dioxide, and the hydrogen combines with oxygen to make water.
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