The energy sector is leading a steep decline in U.S. stocks as the price of oil slumps again.
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The euro also sank to a nine-year low Monday as traders worried about whether Greece will stay in Europe's currency union.
The Dow Jones industrial average slide 228 points, or 1.3 percent, to 17,604 as of 11:45 a.m. Eastern time.
The Standard & Poor's 500 index fell 27 points, or 1.3 percent, to 2,030. The Nasdaq composite fell 43 points, or 0.9 percent, to 4,683.
Energy companies had the worst declines in the S&P 500 index. Denbury Resources and Noble Energy each lost 9 percent.
Crude oil dropped $2.40 to $50.30 a barrel.
U.S. government bond prices rose. The yield on the 10-year Treasury note fell to 2.05 percent.