Why Did President Polk Alter His Battle Strategy in the Mexican-American

Why did President Polk alter his battle strategy in the Mexican-American War and decide to target Mexico City?

A) Native Americans helped Mexican soldiers defeat the Americans in the borderlands.
B) Despite heavy losses on the battlefield,Mexico refused to trade land for peace.
C) Polk sought a dramatic victory to prevent U.S.soldiers from deserting the army.
D) Santa Anna surrounded the American troops at Veracruz.