The correct answer is true.
It is true that skyscrapers and mass transit, which were developed in the late 1800s, contributed to the size of large cities in America.
In the late 1800s, modern and larger cities represented an attractive place to live in the United States. These cities had the infrastructure for better living conditions, factories that offered jobs, better roads, new houses, different kind of shops, tall buildings called skyscrapers and better transportation. Good examples of these kinds of cities were New York or Chicago.