WASHINGTON (AP) — Since the Federal Reserve raised interest rates from record lows last month, the global picture has darkened. SAN FRANCISCO (AP) — Four of Twitter's key executives are leaving the company in an exodus that has escalated the uncertainty facing the messaging service as it struggles to broaden its audience and lure back disillusioned investors. The upheaval leaves Twitter without its top engineering executive, top products executive, its head of human resources and leader of the company's media partnerships. Sales at the world's biggest hamburger chain rose 5.7 percent in the U.S.