The correct answer is D. Immigrants and African Americans
Step-by-step explanation:
The Transcontinental railroad in the U.S. was a network of railroads that crossed the country and connected the areas in the Pacific Coast with those in the East. These railroads were built in the 19th century and guaranteed a cheaper and faster way to travel and transport goods.
In terms of construction, the first Transcontinental railroad took six years to be built; it was financed by both the government and private companies; and in this, mainly immigrants and Africans Americans participated. Indeed, Chinese immigrants and immigrants of other places played an important role in the construction of this railroad and also, it was common African Americans were hired as most were scaping after the end of the Civil War.