NEW YORK (AP) — Stocks are falling in morning trading Tuesday following mixed earnings news from U.S. companies. Investors are waiting for testimony from Federal Reserve Chair Janet Yellen on the economy later today. A new report showed that housing prices rose in March, but at a slower pace than a month earlier.

KEEPING SCORE: The Dow Jones industrial average fell 79 points, or 0.5 percent, to 16,451 as of 11:19 a.m. Eastern time. The Standard & Poor's 500 index dropped seven points, or 0.4 percent, to 1,877. The Nasdaq composite fell 21 points, or 0.5 percent, to 4,117.

TWITTER TUMBLE: The instant messaging service plunged $4.45, or nearly 12 percent, to $34.31 after Twitter insiders were allowed to sell stock for first time on Tuesday since the company's IPO in November. The company said last month that some key insiders, such as CEO Dick Costolo, did not plan to sell stock when the lock-up period expired. Twitter is down by more than half from its high of $74.73 in December.

INSURER WOES: American International Group fell $1.62, or 3 percent, to $51.10. The company reported revenue that was below what investors were expecting due to higher catastrophe losses and lower investment income.

OFFICE DEPOT UP: The office supply chain soared 70 cents, or 17 percent, to $4.87 after reporting adjusted profits for the first quarter that were twice as high as analysts had expected. The company also said it would close at least 400 U.S. stores after its merger with OfficeMax resulted in overlap of retail locations.

HOME PRICES: U.S. home prices rose at a slightly slower pace in the 12 months that ended in March, according to data provider CoreLogic. It's another sign that weak sales, caused in part by rising mortgage rates, have begun to restrain the housing market's sharp price gains. Home builder stocks fell broadly. Ryland Group fell $1.25, or 3 percent, to $37.51 and D.R. Horton fell 64 cents, or 3 percent, to $22.34.

ANOTHER BIG PHARMA DEAL: Merck fell $1.28, or 2 percent, to $57.35 after the drug company agreed to sell its non-prescription medicine and consumer-care business to Germany's Bayer for $14.2 billion. Products in that business include Claritin allergy pills, Coppertone sunscreen and Dr. Scholl's footcare products.

MORE EXPORTS: The U.S. trade deficit narrowed in March as exports rose to the second highest level on record, led by gains in sales of aircraft, autos and farm goods. The deficit declined to $40.4 billion, down 3.6 percent from a revised February imbalance of $41.9 billion, the Commerce Department reported. The February deficit had been the biggest trade gap in five months.

EUROPE: In Europe, both Germany's DAX and the CAC-40 in France fell by 0.7 percent. Britain's FTSE-100 lost 0.4 percent.

BONDS AND OIL: U.S. government bond prices rose slightly. The yield on the 10-year Treasury note fell to 2.60 percent from 2.61 percent Monday. The yield is close to its lowest of the year and has fallen from 3 percent at the start of January. The price of oil rose 16 cents, or 0.2 percent, to $99.64 a barrel.