Answer:
Step-by-step explanation:
The answer is C. transcontinental railroad.
The transcontinental railroad, completed in 1869, played a significant role in enabling the population shift to the West in the late 1800s. It provided a fast and efficient mode of transportation, connecting the eastern and western parts of the United States. This transportation infrastructure opened up new opportunities for settlement, trade, and economic growth in the western regions. The transcontinental railroad made it easier for people to travel to the West, leading to a massive increase in the number of individuals heading in that direction during that time period.