The right answer is D) to replace Eastern European immigrants lured by gold mining.
The Transcontinental Railroad in Sacramento, California started in 1864. By this time the workforce was primarily formed of unemployed gold miners and European immigrants, especially Eastern Europeans. But their behavior demonstrated unstable and unreliable. This problem forced the company to look for another source of labor. They found what they were looking for in the labor of Chinese people. Because of their temporary status and dream of a good life back in China apparently made them more willing than American laborers to endure the low pay of railroad work and the dangerous working conditions. Nearly 11,000 Chinese workers helped on the construction efforts.