The correct answer is D) by passing unfair tax laws that penalized them.
Whites gained more power over Mexicans who stayed in the United States after the Mexican American War by passing unfair tax laws that penalized them.
After the Mexican-American Revolution, the Treaty of Guadalupe-Hidalgo gave three options for Mexicans that wanted to stay in the United States territory. If Mexicans decided to stay and not to leave, they became United States citizens, but the U.S. government was going to decide when and to what extent. The reality was that Mexicans that decided to stay were treated as visitors, not as U.S. citizens. For instance, Mexicans that decided to stay could not vote in that time.