The exhaust pipes of a VW diesel car are photographed in Frankfurt, Germany, on Wednesday. German auto bosses, ministers and state governors are considering how to reduce diesel emissions as drivers face the threat of possible bans on driving older diesel cars in some cities. Michael Probst/AP hide caption

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Michael Probst/AP

BMW's electric i3 Concept is presented before the Paris Motor Show last September. The car was officially unveiled Monday; purchasers can reportedly opt for using a gas-powered SUV several weeks each year. AFP/AFP/Getty Images hide caption

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AFP/AFP/Getty Images