To what location does the airport code SLU refer?

The airport code SLU refers specifically to George F. L. Charles Airport, which is located in St. Lucia. The use of airport codes is standardized by the International Civil Aviation Organization (ICAO) and the International Air Transport Association (IATA), where each code is unique to its corresponding airport. In this case, SLU is recognized internationally as the code for this particular airport in St. Lucia, making it the correct answer.

The other options represent different locations with different airport codes. For example, Chicago has several airports, but none are represented by SLU, and similarly, Charleston and Cedar Rapids have their own unique identifiers as well. Understanding the system of airport codes can help in navigating travel and identifying air travel routes effectively.