Audi is exploring options to keep selling its five-cylinder engine in Europe, including hybridization, according to the U.K.'s Autocar.The Audi RS3 has already been taken off sale in Europe ahead of the Euro 7 emissions regulations, which the inline-five does not comply with.The RS3 is one of just two vehicles that use the 2.5-liter engine, making it tricky to justify the costs of upgrading it to meet Euro 7.