Answer:
A
Step-by-step explanation:
"Americans must rule America" implies that any immigrants that are not born in the United States should not serve in the government.
Additionally, the phrase is immediately followed up by "native-born citizens should be selected for all State, Federal, and municipal offices of government employment, in preference to all others," which elaborates on how we might enforce that.
Knowing this, non-"Americans" are clearly not welcome by the "Know-Nothing Party", so it's not B or C.
While C is more correct than B, not all citizens are native-born. So, the "Know-Nothing Party" does not believe that all citizens should have an equal chance.
Since it's not B or C, it must be A.