Which airport code refers to Calgary?

The airport code that refers to Calgary is YYC. This code follows the International Civil Aviation Organization (ICAO) standards, where Canadian airports often utilize a 'YY' prefix along with a letter representing the city or region. Calgary International Airport, in particular, is designated with the letters 'YC,' which comes from the city's name, giving it the full code YYC.

The other options do not correspond to Calgary. RDU is the airport code for Raleigh-Durham International Airport in North Carolina, RSW is for Southwest Florida International Airport, and AF does not correspond to any airport in the commonly used systems for identifying airport codes. Thus, YYC is clearly identified as the correct code for Calgary International Airport.