The correct answer is B) Building railroads in western territories.
Irish and Chinese immigrants are best remembered for performing the following type of labor during the late nineteenth century: "Building railroads in western territories."
At the end of teh 1800s, these two groups of immigrants -Chinese and Irish- found cheap jobs working for the two railroad companies that were constructing the famous Transcontinental Railroad that was going to connect the Easters states of the United States with the Pacific states.
Yes, the Transcontinental Railroad was constructed by the Union Pacific Railroad and the Central Pacific, as part of the Pacific Railroad Act of 1862.
The Transcontinental Railroad was inaugurated on May 10, 1869, in the city of Promontory Utah.