Justice Department Studying Microsoft-Yahoo Venture

As the U.S. Justice Department reviews the proposed partnership, approval figures to hinge on this question: Will the online ad market be healthier if Google's dominance is challenged by a single, more muscular rival instead of two scrawnier foes? The first step toward getting an answer came this month when Microsoft and Yahoo filed paperwork with federal regulators to comply with the Hart-Scott-Rodino Act, an antitrust law governing mergers and alliances between competitors.