The combined Union Pacific-Central Pacific line became known as the First Transcontinental Railroad and later the Overland Route. The line was constructed primarily by Irish labor who had learned their craft during the recent Civil War.
Factories? Im not very sure because this is kinda vague. but hopefully you can get it!
C. Using government spending to stimulate the American economy.
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Earth's mass has remained constant, and thus the gravitational pull at the surface has decreased over time; Earth's mass has grown with the volume in such a way that the surface gravity has remained constant; Earth's gravity at its surface has increased over time, in line with its hypothesized growing mass and volume.
B. Senator Joe McCarthy lasting from the late 1940s through 1950s.