A.I. Explanation:

First sentence: Why this is the first line? This paragraph is the first because it introduces the main topic of the text, which is the Great Wall of China. It gives a broad overview of its importance. This follows the rule of Topic Sentence. Why other lines are not chosen? Paragraph 2 starts with "It" which is a pronoun and needs context. Paragraph 3 starts with "It was built" which also needs context. Paragraph 4 starts with "The emperor" which refers back to someone not yet introduced. Paragraph 5 starts with "He" which is a pronoun needing context.

Concluding sentence: Why this is the last line? This paragraph is the last because it wraps up the story of the Great Wall's construction. It gives a final detail about the wall's history and shows how it was built over time. This follows the Summary Style rule, as it brings together the earlier points.

Paragraph pairs:

• Pair 1 (Paragraph 1 → Paragraph 2): Paragraph 2 connects to Paragraph 1 because it gives more details about the Great Wall. This follows the Broader to Specific Strategy, where the first sentence gives a general idea and the second gives specific information.
• Pair 2 (Paragraph 2 → Paragraph 3): Paragraph 3 connects to Paragraph 2 because it explains who built the wall and why. This follows the Logical Order rule, where the information flows from the description of the wall to its history.
• Pair 3 (Paragraph 3 → Paragraph 4): Paragraph 4 connects to Paragraph 3 because it talks about the emperor's actions in building the wall. This follows the Object Subject Strategy, where the subject of the previous paragraph (the emperor) becomes the focus of the next.
• Pair 4 (Paragraph 4 → Paragraph 5): Paragraph 5 connects to Paragraph 4 because it gives more details about what the emperor did. This follows the Logical Order rule, where the explanation of the emperor's actions continues.