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Traders work on the floor of the New York Stock Exchange.
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Traders work on the floor of the New York Stock Exchange.

Check out which companies are making headlines before the bell:

Aetna — The health insurer earned an adjusted $1.37 per share for its latest quarter, 16 cents above estimates, with revenue also beating forecasts. Aetna was helped by improved membership numbers and margins in its Medicare business. However, it is also projecting full year 2016 earnings of $7.75 per share, below estimates of $8.05 a share.

Questar — The natural gas producer is being bought by Dominion Resources for $25 per share in cash, or about $.4 billion. Questar had closed Friday at $20.39 per share.

Cardinal Health — The drug distributor earned an adjusted $1.30 per share for its latest quarter, 4 cents above estimates, with revenue also above analysts' forecasts. The company said its results were boosted by growth in its customer base and solid fundamentals, among other factors.

Twitter — The Information's Jessica Lessin reports that investor Marc Andreessen and Silver Lake Partners have considered a deal for Twitter, whose stock has been battered in recent weeks.

Restoration Hardware — Cowen downgraded the home furnishings retailer to "market perform" from "outperform," citing a slowdown in high end consumer spending and a promotional environment.

AIG — The insurance company was downgraded to "market perform" from "outperform" at BMO Capital Markets, saying AIG will have a tough time delivering on the financial targets announced last week in AIG's new strategic plan.

Blackstone — The asset manager is reportedly seeking buyers for information technology outsourcing firm Pactera, one of its biggest China-based assets. Dow Jones reports Blackstone could get up to $1 billion for Pactera.

Monster Beverage — The energy drinkmaker's stock was upgraded to "outperform" from "market perform" at Wells Fargo. That follows recent weakness in the shares, plus the results of a Wells Fargo survey showing U.S. distribution issues are largely resolved.

American Airlines Group — Cowen upgraded the airline's stock to "outperform" from "market perform," saying it sees American's key metrics improving sequentially throughout the year.

Chipotle Mexican Grill — The Centers for Disease Control and Prevention is expected to declare as soon as today that the restaurant chain's E. coli outbreak is officially over.

Tesla Motors — Chief Executive Officer Elon Musk has increased his investment in the electric car maker. Musk exercised 532,000 Tesla stock options last week, and covered the taxes with cash rather than selling some of his current holdings.

Boeing — Boeing won the contract to begin preliminary work on a new fleet of Air Force One presidential jets, based on its 747-8 model. The initial contract is worth $25.8 million, while estimates put the deal's total worth at $1.65 billion.

Nokia — Nokia settled a long-running patent dispute with Samsung, but the shares are under pressure on investor disappointment over the financial terms of that deal.

HSBC — HSBC is imposing a global hiring and pay freeze, according to Reuters.

Las Vegas Sands, Wynn Resorts — These are among casino operators on today's watch list, following word that gambling revenue in Macau dropped 21.4 percent in January compared to a year earlier, putting it near a five-year low.

Barclays, Credit Suisse — The two companies have settled with New York State and with the Securities and Exchange Commission in a case that had alleged that the banks misled investors in their so-called "dark pools." The banks will pay a combined total of $154.3 million.

Herbalife — Neither Herbalife nor investor Bill Ackman were found to have engaged in activity to support criminal charges, according to The Wall Street Journal. Ackman continues to maintain that the nutritional products company is nothing more than a pyramid scheme.

Coca-Cola — Coca-Cola took a 40 percent stake in Nigerian juice and snack Chi as it continues its push into Africa.

Toyota Motor — Toyota may halt production at its Japanese plants this month because of a steel shortage. That shortage stems from an explosion at the Aichi Steel plant that has impacted production of steel auto components.

Yahoo — Chief Executive Officer Marissa Mayer is not planning to leave the company, according to the New York Post, which also said this week's earnings may be better than many analysts expect. (Disclosure: CNBC has a content-sharing partnership with Yahoo's finance site.)

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