Which cities have served as host cities? | Do you want the names of the cities who served as host cities? | Yes.
SELECT distinct T1.city FROM city AS T1 JOIN hosting_city as T2 on T1.city_id  =  T2.host_city
cities that have served as host cities refers to SELECT DISTINCT city FROM a table that associates cities with their hosting status; joining city information with hosting status through a common identifier (e.g., city_id).