Which airport code is for a city located in Iowa?

The airport code DSM refers to Des Moines International Airport, which is indeed located in Iowa. Each airport code consists of three letters as designated by the International Civil Aviation Organization (ICAO) or the International Air Transport Association (IATA), and these codes can reflect the city's name or an abbreviation associated with the location. In this case, DSM directly correlates to Des Moines, making it the correct choice for an airport located in Iowa.

The other options represent airports in different states; for example, FSD stands for Sioux Falls Regional Airport in South Dakota, GJT is Grand Junction Regional Airport in Colorado, and COS represents Colorado Springs Airport in Colorado. Thus, while these may also be valid airport codes, they do not pertain to any city in Iowa.