Which of the following is a sustainable practice in which people build small gardens on rooftops or in vacant lots?

Two gymnastics teams are intense rivals. the first team has started recruiting new gymnasts from different cities and even foreign countires in an effort to build a stronger team. after learning this, the secondteam begins its own recruitment campaign to find better gymnasts. over a period of months, each team recruits dozens of players, each time trying to find a better recruit than its rivals most recent addition. which idea from the cold war is most similar to this scenario