Irish and chinese immigrants worked hard to construct the

O: Transcontinental Railroads

Explanation:

I remember reading about it in history class

"a shortage of traditional labor created new opportunities in the workplace. a major cause of the internment of japanese americans during world war ii was. racial prejudice. in the early 1940's, the "destroyers-for-military-bases deal" with great britain and the lend-lease act were evidence that the united states."