Final answer:
The correct answer is option c) Chinese immigrants.
Step-by-step explanation:
Before the arrival of the "Okies," or migrants from the Oklahoma region during the Dust Bowl era, several groups of workers served as migrant labor in the United States. These included Mexican immigrants, Filipino immigrants, and Chinese immigrants. All these groups, at different points in time, contributed to the U.S. economy through various forms of manual labor, primarily in agriculture and railroad construction.
The Chinese immigrants, in particular, were significant for their contribution to the construction of the Transcontinental Railroad and were actively sought for their labor before being subjected to severe discrimination which included the passage of the Chinese Exclusion Act in 1882, banning immigration from China.