Final answer:
Asian immigrants, primarily Chinese, came to the Pacific region during the Gold Rush and found jobs building the Transcontinental Railroad when gold became hard to find.
Step-by-step explanation:
The Gold Rush in 1849 led to a significant migration of people, including many immigrants from Asia, to the West in search of prosperity. The correct answer to the question is 'c) Asians, railroad.' Many of these immigrants were Chinese, and with gold becoming more challenging to find, they sought employment in other industries. They played a crucial role in building the Transcontinental Railroad, taking on arduous and dangerous work. This effort was instrumental in the completion of the railroad, which was central to the development of transportation and commerce across the United States.