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Now Playing: 05-01-12 Marketplace Morning Report

Exxon Mobil trades off with Apple as the top company in the U.S., but most Americans still know very little about it. A new book out today could change that. Later this morning, we'll find out whether the big auto companies were still selling lots of cars in April. And what do high sales mean for auto workers? Meanwhile, Delta Air Lines is buying an oil refinery in an attempt to cut costs.