Stock futures were slightly lower on Tuesday morning ahead of a speech from Federal Reserve Chair Janet Yellen. 

S&P 500 futures fell 0.28%, Dow Jones Industrial Average futures slipped 0.24%, and Nasdaq futures declined 0.21%.

Yellen is scheduled to address the Economic Club of New York on Tuesday about monetary policy and the economic outlook for the U.S. economy. Investors will parse Yellen's comments for clues as to when the central bank could next raise interest rates.

At its recent March meeting, the Fed downgraded its forecasts to two rate hikes this year from four. However, recent comments from Fed members such as St. Louis Fed President James Bullard suggested an April rate hike isn't off the table. 

The hijacking of a domestic Egyptian flight and subsequent hostage situation came to a close Tuesday with the hijacker surrendering, according to reports. An Egyptian man hijacked an EgyptAir flight overnight, forcing the plane to land in Cyprus. Officials have assured that the incident isn't related to terrorism but instead to the hijacker's ex-wife. The situation added fears over the vulnerability of airline security just a week after a terrorist attack in Brussels. 

The standoff between the FBI and Apple (AAPL - Get Report) abruptly ended on Monday after prosecutors asked a federal judge to vacate a disputed order for Apple to break into a phone used by the San Bernardino terrorists. The FBI said it had used an alternative method to unlock the phone, though did not divulge its workaround. The case had triggered debate over whether Apple should acquiesce and potentially weaken all customers' security. 

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Yahoo! (YHOO)  reportedly has given potential buyers an April 11 deadline to submit bids for its core Internet business and Asian assets, such as its stakes in Alibaba (BABA - Get Report) and Yahoo! Japan. The company is looking to narrow the field to around 40 bidders.

SunEdison (SUNE) tanked nearly 30% in premarket trading on reports the Securities and Exchange Commission is investigating whether the company misled investors over its liquidity position. Regulators are reportedly looking into whether the claim it had $1.4 billion in cash last year during a share price collapse was accurate.

Lennar (LEN - Get Report)  climbed more than 2% after topping analysts' estimates on its top- and bottom-lines during its fiscal first quarter. The homebuilder earned an adjusted 63 cents a share, 11 cents above estimates, while revenue of nearly $2 billion surged 21% from a year earlier. 

McCormick ( MKC - Get Report) added 1.3% after raising its outlook following a better-than-expected first quarter. The spices company expects sales to climb 1% to 3% this year, or between 4% and 6% on a constant-currency basis. First-quarter profit jumped 32% thanks to acquisitions and cost-cutting efforts.