What was the Triple Alliance in the Aztec Empire?

I - The Triple Alliance was formed by the cities of Texcoco, Tlacopan, and Azcapotzalco.
II - The Triple Alliance was initially conceived as an alliance of three autonomous city-states.
III - The cult of Huitzilopochtli was the imperial cult of the Triple Alliance.
IV - The Triple Alliance was defeated by the Spanish in 1521.
a) I and II are correct.
b) II and III are correct.
c) III and IV are correct.
d) I, II, and III are correct.
e) II, III, and IV are correct.