The correct answer is A: because of the changed border, many Mexicans became Americans.
The Mexican-American War (1846-1848) resulted in significant territorial changes, with the United States acquiring large portions of Mexico's territory (including present-day California, Arizona, New Mexico, Nevada, Utah, and parts of Colorado and Wyoming). As a result, many people who lived in these newly acquired areas became U.S. citizens, thereby increasing the number of Hispanics living in the United States.