The correct answer is: "the main reason used by nativists to request anti-inmigration legislation was that Asian immigrants were stealing jobs from US citizens".
Nativism was a political stream that promoted the interests and rights of national population over immigrants. It supported the establishment of measures to control (to block) immigration flows, specially of Chinese immigrants.
Such feelings against imigration were justified by nativists because of the amount of money that such immigrants cost to the public agencies, because they came and worked in jobs that should pertain to domestic citizens, or because they were condenmed to isolation, as they did not know the language or customs of their home country.