During the Mexican-American War, the US pushed the Mexican army as far south as far south as before a treaty was signed
A El Paso, TX
B. Phoenix, AZ
C. Mexico City
D. the Rio Grande

Option C. Mexico City  is the correct one.

Explanation:

Option C is the only correct option as the American troops managed to enter Mexican territory as far as into Mexico City. That happened in 1847 when General Winfield Scott even laid siege to the city.

Eventually the peace treaty of Guadalupe Hidalgo was signed.

All other options are not correct as they were either a part of United States by then or were already breached.

answer; ///(positive correlation);