Wall Street closing mixed Thursday

In U.S. economic news, Federal Reserve (Fed) chair Janet Yellen reiterated her commitment to keep interest rates low until the economy is on firmer footing. She made her comments when appearing before the Senate Budget Committee. It was more or less an encore of her remarks Wednesday to the Joint Economic Committee of Congress. In international economic news, European markets finished higher and nearly all Asian markets closed with gains. In corporate news, shares of Tesla sank over 11 percent in volatile trading. The company's earnings beat expectations Wednesday, but Tesla forecast that expenses will continue to rise as it expands into China, develops its next vehicle, and breaks ground on a new factory. The Keurig Green Mountain coffee machine was on overdrive. Shares spiked 13 percent after the company posted double-digit sales and earnings growth for the first quarter. The company also announced the expansion of its partnership with the J.M. Smucker Company. Tiffany & Co shares had some extra glow after the luxury retailer got a 'buy' rating from Bank of America Merrill Lynch. The stock ended the day 2.5 percent higher.