Which two immigrant groups were instrumental in building the transcontinental railroad?

The correct answer identifies the Irish and Chinese immigrant groups as crucial to the construction of the transcontinental railroad. During the mid-19th century, the United States saw a significant influx of Irish immigrants, many of whom were fleeing the Great Famine in Ireland. They contributed a substantial labor force, often taking on some of the most demanding and dangerous jobs involved in building the railway.

Simultaneously, a large number of Chinese laborers also played a pivotal role, particularly in the western segments of the railroad. After the discovery of gold in California, many Chinese immigrants arrived in search of opportunities, finding employment in railroad construction. They were known for their hard work, resilience, and skills, which were vital in overcoming the challenges posed by the Sierra Nevada mountain range and other difficult terrains.

While the other options list groups that have contributed to various sectors of American society, they were not primarily associated with the transcontinental railroad construction. The historical significance of the Irish and Chinese in this context highlights their contributions to the economic development of the United States during that era.