I'm pretty sure the answer is A. Bird
The sentence from the introduction paragraph that serves as the author's thesis is: "<em>Yet key technological developments caused a rapid growth in American urban areas</em>."
A thesis statement is, by definition, the sentence that captures the main idea and your point of view on it on your article.
The sentence that I believe best represents what the author meant to present to the readers is one that briefly explains his view on the topic mentioned in the title, which is the positive effect of technological advancements on a city's growth.
