Hot electric vehicle stock Nio drops 14% after Goldman downgrades to sell

The NIO Inc. ES6 electric sport utility vehicle (SUV) stands on display at the Auto Shanghai 2019 show in Shanghai, China, on Tuesday, April 16, 2019. China's annual auto show, held in Shanghai this year, opened to the media on Tuesday amid the specter of an electric-car bubble and as the world's largest auto market trudges through its first recession in a generation. Photographer: Qilai Shen/Bloomberg via Getty Images

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Tesla rival Nio's U.S.-traded shares dropped more than 14% on Friday after Goldman Sachs downgraded the stock to a sell rating, citing valuation concerns after the company's more than 60% rally over the last month.