A.I. Explanation:

First sentence: Why this is the first line? This paragraph is the first line because it gives a broad overview of how settlements were built in the past. It introduces the main topic of the text, which is about urban planning and safety. It does not use any pronouns or definite articles that need prior context. Why other lines are not chosen? Paragraph 2 starts with "Cities" which is a specific noun and does not stand alone. Paragraph 3 starts with "Urban planners" which is also specific and needs context. Paragraph 4 starts with "If the dangers" which is a conditional phrase and does not stand alone.

Concluding sentence: Why this is the last line? This paragraph is the last line because it provides a solution to the problems discussed earlier. It wraps up the ideas by showing what can be done about the threats. It concludes the discussion on urban planning.

Paragraph pairs:

• Pair 1 (Paragraph 1 → Paragraph 2): Paragraph 2 connects with Paragraph 1 because it continues the idea of settlements. It shows how cities moved from higher ground to lower areas, which are now at risk. This is a logical order of ideas.
• Pair 2 (Paragraph 2 → Paragraph 3): Paragraph 3 connects with Paragraph 2 because it talks about what urban planners need to do after explaining the risks. It shows a cause and effect relationship: cities are at risk, so planners must act.
• Pair 3 (Paragraph 3 → Paragraph 4): Paragraph 4 connects with Paragraph 3 because it gives a solution to the threats mentioned. It explains what planners can do if the dangers are specific, showing a logical order of problem and solution.