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 Roman Empire. It gives a broad overview of the empire's importance and its time period. This follows the rule of Topic Sentence. Why other lines are not chosen? The other paragraphs are not chosen because they do not stand alone. For example, Paragraph 2 starts with 'It began,' which is a pronoun and needs context. Paragraph 3 starts with 'The fall,' which also needs prior information. Paragraph 4 starts with 'Roman law,' which assumes knowledge of the Roman Empire. All these reasons make them not independent.

Concluding sentence: Why this is the last line? This paragraph is the last because it concludes the discussion about the Roman Empire. It shows the result of the empire's fall, which is the start of the Middle Ages. This follows the rule of Conclusive Words, as it wraps up the main ideas presented in the previous paragraphs.

Paragraph pairs:

• Pair 1 (Paragraph 1 → Paragraph 2): Paragraph 2 connects to Paragraph 1 because it gives more details about the Roman Empire. This follows the Broader to Specific Strategy. The first paragraph talks about the empire's significance, and the second paragraph explains when it started and how it grew.
• Pair 2 (Paragraph 2 → Paragraph 3): Paragraph 3 connects to Paragraph 2 because it shows the impact of the Roman Empire. This follows the Logical Order rule. The second paragraph talks about the empire's growth, and the third paragraph explains how its laws affected later systems.
• Pair 3 (Paragraph 3 → Paragraph 4): Paragraph 4 connects to Paragraph 3 because it discusses the end of the Roman Empire. This follows the Cause and Effect Relationship rule. The third paragraph talks about the influence of Roman law, and the fourth paragraph explains what happened after the empire fell.