Many Mexicans who lived on land that was part of the Mexican Cession A) had to give up their land and relocate to Mexico.
B) became US citizens and added to the area’s population.
C) were not allowed to own property in the United States.
D) fought the Americans even though the war was over.

I think it's B. they became US citizens and added to the areas population.

Explanation:

"Under Article VIII and IX of the Treaty of Guadalupe Hidalgo, Mexican citizens living in the areas of the Mexican Cession were promised protection of their property rights and could choose to become American citizens which would be given to them within one year." Mexicans, Manifest Destiny.

they united the colonies in their fight against the british.

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