Falling oil prices and good corporate news buoyed stocks last week, extending a three-week rally. As crude oil prices dropped below $58 a barrel on Friday—the lowest levels since summer—General Motors announced it had reached an agreement with the United Auto Workers on health-care contributions. The news boosted the Dow, which finished the week at 10,686.04, up nearly 155 points, a nearly 1.5 percent increase. The Nasdaq gained 28.22 points to close at 2202.47, up 1.3 percent. Advertising stocks, however, closed mixed. Omnicom closed flat at 83.11, while WPP Group, trading as American Depository Receipts, finished the week up 0.56 points to close at 50.67, a 1 percent gain. After reporting a $100 million net loss for the third quarter and a $240 million loss for the fiscal year last Wednesday, Interpublic Group dropped 6.6 percent (0.7 points) to close at 9.96.