Final answer:
The Transcontinental Railroad was mainly built by Chinese immigrants who faced challenging and underpaid conditions but displayed resilience and efficiency in their work. The correct option is b. Chinese immigrants
Step-by-step explanation:
The Transcontinental Railroad was predominantly constructed with the labor of Chinese immigrants, alongside a minority of Irish and other immigrant groups.
The Chinese workers, who were the first Asian immigrants in the mid-nineteenth century, played a critical role in building the railroad, particularly over the difficult Sierra Nevada mountain range.
They faced grueling and underpaid work conditions, often taking on the most hazardous tasks. Despite these challenges, they demonstrated resilience and efficiency, contributing significantly to one of the nineteenth century's greatest American engineering feats. The correct option is b. Chinese immigrants