Why Were the 1985 Earthquakes in Mexico City a Watershed

Why were the 1985 earthquakes in Mexico City a watershed in Mexican politics?

A) Groups learned that they could solve their problems better without the Mexican government than with it.
B) Armed militias who challenged the legitimacy of the government emerged.
C) The swift and efficient response of the Mexican government reinforced the legitimacy of the PRI.
D) The massive relief efforts of the United States helped to ease the tensions between the two states.
E) They led to the defeat of the PRI in the 1988 elections.