U.S. stocks moved higher on Wednesday with the Dow Jones Industrial Average closing in on the critical 20,000 level. The blue-chip index has been flirting with the threshold for a few weeks. Vitamin and health shop GNC Holdings (GNC) - Get Report is set to close 4,400 stores in the U.S. After the closures, the company is changing its pricing scheme, with protein powders, nutritional supplements and herbal remedies all priced at the same level. The company faces tough competition from the likes of Walmart (WMT) - Get Report . Delta Air Lines (DAL) - Get Report has cancelled its order of 18 Boeing (BA) - Get Report 787 Dreamliner aircraft. The order was placed by Northwestern Airlines, which was acquired by Delta in 2008. The airline is purchasing multiple 737-900ER jetliners, a single-aisle plane from Boeing.