What major national-level development happened in the late nineteenth century?

There were many national level developments in the late-nineteenth century. Perhaps the most important was the development of the light bulb by Thomas Edison. Edison's invention revolutionized all aspects of American life ranging from work to leisure. It also inaugurated the modern electrical industry.

theodore roosevelt 26th u.s. president : i admire his energy and passion. he was a fundamentally good man, brilliantly intelligent, possessed of extraordinary will and ability, supremely self-confident, bold, egalitarian, idealistic…. , lord, can we have him back?

the answer is definitley b!