A.I. Explanation:

First sentence: Why this is the first line? This paragraph is the first line because it introduces the main topic of the American Regionalism movement. It gives a broad overview of when this movement started and how it grew. This fits the rule of Topic Sentence. Why other lines are not chosen? The other paragraphs do not qualify as the first sentence. For example, Paragraph 2 starts with 'The Civil War', which is specific and does not introduce the main topic. Paragraph 3 uses 'When the national government', which is not general. Paragraph 4 starts with 'In addition', which is a conjunction and shows it is not independent.

Concluding sentence: Why this is the last line? This paragraph is the last line because it wraps up the discussion about the changes in society after the Civil War. It summarizes how people adapted to new cultures, which reflects the overall theme of the text.

Paragraph pairs:

• Pair 1 (Paragraph 1 → Paragraph 2): Paragraph 2 connects to Paragraph 1 because it explains the main factor that influenced the American Regionalism movement. This follows the Broader to Specific Strategy, where the first paragraph gives a general idea and the second provides a specific reason.
• Pair 2 (Paragraph 2 → Paragraph 3): Paragraph 3 connects to Paragraph 2 because it gives more detail about the Civil War. It shows the cause and effect relationship, where the Civil War is the cause and the effects are explained in the next paragraph.
• Pair 3 (Paragraph 3 → Paragraph 4): Paragraph 4 connects to Paragraph 3 because it continues the discussion about changes after the Civil War. It uses the Connector strategy with 'In addition', showing that it adds more information about the effects of the Civil War.