The correct answer to this open question is the following.
Although there are no options attached we can comment on the following.
Immigrants from China made up a large portion of the labor force during the California gold Rush for the following two reasons:
1) They arrived at the port of San Francisco, California, from China. 2) They worked as miners in the California gold mines and were paid low salaries, working under extremely unhealthy and risky conditions.
Chinese immigrants were treated badly because they were foreigners in a foreign land. White miners were jealous of the Chinese miners because Chinese miners worked very hard and were more efficient.
Years later, in the 1860s, and with the passing of the Pacific Railroad Act, Chinese people worked in the Transcontinental Railroad.
