The Hub for Air Travel Is the Busiest Hub in the World

The letters a t c are the abbreviation of air traffic control, or air traffic controller. The pilot can't go anywhere until the control tower and the air traffic controllers there have given him or her permission to do so. Another important word to know is hub - the hub for air travel is the busiest airport. Rese in 20 21 by passenger numbers, not cargo, passenger numbers. Can you name one of the three busiest hubs in the world?