Twitter, Discovery and Mylan are the Yahoo Finance charts of the day.

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Twitter (TWTR): Shares are up in early trade, at around 5.2%. The stock rose for the social media company on news that it will replace Monsanto in the S&P 500 index.

Discovery (DISCA): Shares up here,  around 3.2%.  The basic cable and satellite television network was upgraded by stock analysts at MKM Partners from a "neutral" rating to a "buy" rating, citing an attractive valuation and potential for growth, among other factors.

Mylan (MYL): Shares up here, at around 7.0%. Shares of the company rose in the premarket after the Food and Drug Administration approved Mylan's drug aimed at reducing the risk of infections following chemotherapy.

 For more on today's big stock movers check out the Final Round, live at 3:55 p.m. ET, right here on Yahoo Finance.

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