Answer:
The correct answer is:
a. were exclusively single men, particularly after the Civil War
Explanation:
After the civil war in the United States of America the construction of the railroad was retaken by the government whereby Chinese immigrants were hired in order to work on the project, they represented around the 90% of the workers including, mining, building, fishing and all the necessary tasks to complete the whole project. After the railroad work was completed chinese workers moved to agricultural tasks.