Shares of Twitter Inc. plunged 17.9% in premarket trading Friday, after Elon Musk tweeted that the deal to buy the social media company was “temporarily on hold.” Musk, the chief executive of electric vehicle maker Tesla Inc. , said the hold on the deal is “pending details supporting calculation that spam/fake accounts do indeed represent less than 5% of users.” Twitter’s stock is on track to open at the lowest price seen during regular-session hours since March 17, which was before Musk first disclosed he had acquired a large stake in Twitter. Tesla’s stock rallied 4.5% ahead of the open.

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