The answer is C. Laws that limited immigration by nationality.
Nativism is the majority's interest over immigrants. The majority did not like immigrants coming into their country so they made laws related to limiting immigrant's access.
It is not A because the Klu Klux Klan flourished as a result of nativity. Many white men hated black people and supported the beliefs of the Klu Klux Klan. In only declined later.