1913
 buenos aires underground begins operating. the urban complex is spread out over  and contains plazas and residential buildings. – final member of “the four”
* – original member of "the four"

challenge episodes
key:
 – artist secured a spot and has remained in "the four". on october 22, 2013, the second single which is also the title track, "young legs" was released. in october 1966, as wing commander, he formed an operational training unit and was the unit's first commanding officer. an interpretive center is open throughout the year. by itself this would not be sufficient to argue for a meaningful connection between the two events. 