The correct answer is A. Chinese and Irish immigrants, and African Americans
Step-by-step explanation:
In the United States, the development of railroad transportation along with the construction of railroads all over the country took place mainly during the 18th and 19th centuries. This included the construction of massive railroad systems such as First Transcontinental Road. In terms of workers, most workers in these constructions were African Americans (former slaves looking for opportunities) or immigrants from countries such as China or Ireland who immigrated looking for better living conditions. For example, the Central Pacific Road was mainly constructed by Chinese immigrants. According to this the groups of people that made up most of the workers on the railroad were Chinese and Irish immigrants and African Americans.