$Delta Air Lines(DAL.US)Delta Air Lines' valuation is too high, while American Airlines' stock price is severely undervalued. It's time to cash in on the booming U.S. economy. The governments of China and the U.S. have agreed to significantly increase flights between the two countries to meet the demand for personnel exchanges. American Airlines' P/E ratio is only about 5 times, indicating a strong need for valuation recovery. Inflation expectations are strong, and currently, the ticket price for China-U.S. flights is 20,000 yuan, far above the historical price range. American Airlines will return to a high stock price range.