Answer:
The urbanization of the United States quickened due to technology improvements.
Step-by-step explanation:
This is the topic sentence of the conclusion, that means it summarizes the information found in the paragraph. As the conclussion is the last paragraph, we can assume that it synthesizes the things stated previously, it points or highlights the most important author's idea.
To confirm this, we can search through the text for the main subjects described. The first prargraph is used to present the ideas and main point of the author. In this case the author states that "Yet key technological developments caused a rapid growth in American urban areas." The main idea is that the technology improvements helped the urbanization process.
The following paragraphs are used to support this idea with evidence.