A four-day surge in the markets ended Friday as falling commodity prices including gold, brought down energy and mining companies. Signs of a slowing economy rattled commodity markets. Crude oil dropped 2 percent to $91 a barrel as weak US economic reports followed forecasts for weaker oil demand. Sales at US retailers fell in March and companies restocked their shelves at a much slower pace in February than in the month before. A measure of consumer sentiment from the University of Michigan also slumped. The weaker reports pushed traders into the safer Treasurys, sending yields near their lows for the year.