A.I. Explanation:

First sentence: Why this is the first line? This paragraph is the first sentence because it gives a general statement about sea level raise and its impact. It does not need another sentence for context. It introduces the main topic of the text. Why other lines are not chosen? Paragraph 2 starts with 'This number', which is a pronoun that refers back to the first sentence, so it cannot be independent. Paragraph 3 starts with 'According to the research', which is a phrase that suggests prior context, so it is not independent. Paragraph 4 starts with 'If sea level raises 1 meter', which is a conditional phrase and does not stand alone.

Concluding sentence: Why this is the last line? This paragraph is the last sentence because it gives the final example of the impact of sea level rise. It wraps up the discussion by showing the worst-case scenario.

Paragraph pairs:

• Pair 1 (Paragraph 1 → Paragraph 2): Paragraph 2 connects to Paragraph 1 because it uses the connector 'This number', which refers back to the number of people affected by sea level rise. This shows a logical order of ideas.
• Pair 2 (Paragraph 2 → Paragraph 3): Paragraph 3 connects to Paragraph 2 because it provides a specific example of how many people will die if sea level raises 50 centimeters. This follows the broader statement in Paragraph 2.
• Pair 3 (Paragraph 3 → Paragraph 4): Paragraph 4 connects to Paragraph 3 because it continues the topic of sea level rise and its effects. It gives another example of how many people will die if the sea level raises even more.