Query: Which boroughs was the Mexico City borough split into?
Context: In 1970 Mexico City was split into four different delegaciones: Cuauhtémoc, Miguel Hidalgo, Venustiano Carranza and Benito Juárez, increasing the number of delegaciones to sixteen. Since then, in a de facto manner, the whole Federal District, whose delegaciones had by then almost formed a single urban area, began to be considered a synonym of Mexico City.