Using the passage, answer the following question: What is the largest airline in the world ?

Context: The largest airlines in the world can be defined in several ways. As of 2022, Delta Air Lines is the largest by revenue, assets value and market capitalization, China Southern Air Holding by passengers carried, American Airlines Group by revenue passenger mile, fleet size, numbers of employees and destinations served, FedEx Express by freight tonne-kilometers, Ryanair by number of routes, Turkish Airlines by number of countries served.

Answer: It's not possible to give a unique answer to this question. The largest airlines in the world can be defined in several ways:

- Delta Air Lines is the largest by revenue, assets value and market capitalization, 
- China Southern Air Holding by passengers carried, 
- American Airlines Group by revenue passenger mile, fleet size, numbers of employees and destinations served, 
- FedEx Express by freight tonne-kilometers, 
- Ryanair by number of routes, 
- Turkish Airlines by number of countries served.