Which major airline merger created what was briefly the world's largest airline in 2008, before being surpassed by the United-Continental merger?

The transportation industry has seen remarkable mergers, acquisitions, and strategic shifts that have shaped today's aviation landscape. Many passengers fly with major airlines without knowing the fascinating corporate histories behind these transportation giants. Test your knowledge about one of the most significant airline mergers in recent history that transformed the competitive landscape of air travel.

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Delta Air Lines and Northwest Airlines
American Airlines and US Airways
Southwest Airlines and AirTran Airways
Alaska Airlines and Virgin America