Which of the following is the airport code for a major city in Spain?

The airport code MAD corresponds to Madrid-Barajas Adolfo Suárez Airport, which serves the capital city of Spain, Madrid. This airport is one of the busiest in Europe and a major international gateway for travelers to and from Spain. The code is derived from the name of the city, making it easily recognizable for travelers and relevant for identifying flights and logistics related to Madrid.

The other options represent airport codes for different locations: MEM is for Memphis International Airport in Tennessee, MFE is for McAllen International Airport in Texas, and MIA is for Miami International Airport in Florida. They are not associated with any cities in Spain, which makes MAD the only appropriate choice for this question.