The correct answer is: "Chinese".
The Central Pacific Railroad connected California and Utah since the 1860s decade. It was constructed as the Western branch of the "First Transcontinental Railroad" located in North America.
<u>Chinese immigrants were a crucial labor source during the construction of the railroad.</u> More and more Chinese men continued arriving and were hired even tough the working conditions were extremely harsh and they received less compensation that their white counterparts.
Explanation:
Causation in history refers to the idea that every historical development was initiated (or caused) by developments that came before.
The answer to y0our question is b