Answer:
The topic sentence in the paragraph is option A ) The rapid increase in national wealth in the early 1920s was a surprising cause of the Great Depression.
Step-by-step explanation:
A topic sentence is usually placed at the beginning of a paragraph, it is considered the most important sentence in it. It summarizes the information and provides a better organization. In this case, option A is the topic sentence because it is giving the reason why the Great Depression occurred, which is the topic of the paragraph. In other words, it is summarizing the topic in one sentence.