Answer:
B. Westward expansion
Explanation:
The transcontinental road in the United States linked the east and the west. In 1949 settlers started to move to the west as a result of the discovery of gold in California, the journey involved was very tiresome and dangerous because people had to travel pass mountains and rivers, but there was another alternative which involves traveling by the sea for about 8 months. This lead to the construction of the international railroad making transportation easier and cheaper
