A.I. Explanation:

First sentence: Why this is the first line? This paragraph is the first sentence because it introduces the main topic of people at risk of flooding. It gives a clear overview of the situation without needing other sentences for context. It does not use any pronouns or definite articles that refer to previous information. Why other lines are not chosen? The other paragraphs are not chosen because they do not stand alone. For example, Paragraph 2 starts with 'This amount,' which refers back to something else. Paragraph 3 uses 'Scientists estimate,' which needs context from earlier sentences. Paragraph 4 mentions 'A sea level rise,' which also needs prior information to make sense.

Concluding sentence: Why this is the last line? This paragraph is the last sentence because it wraps up the discussion about sea level rise and its impact. It gives a final thought on the topic, showing the biggest risk and future predictions.

Paragraph pairs:

• Pair 1 (Paragraph 1 → Paragraph 2): Paragraph 2 connects to Paragraph 1 because it uses the connector 'This amount.' It shows that the number of people at risk can change, linking the two ideas.
• Pair 2 (Paragraph 2 → Paragraph 3): Paragraph 3 follows Paragraph 2 logically because it gives a specific estimate about how many more people could be at risk. This shows a broader idea from Paragraph 2 becoming more specific.
• Pair 3 (Paragraph 3 → Paragraph 4): Paragraph 4 connects to Paragraph 3 because it discusses a larger sea level rise. It shows a logical order from the smaller estimate to a bigger risk.