A.I. Explanation:

First sentence: Why this is the first line? This paragraph is the first sentence because it introduces the main topic of mountains. It tells us how mountains are made. It does not need other sentences to understand it. It is a general statement about mountains. Why other lines are not chosen? Paragraph 2 starts with 'This ongoing process', which needs more context. Paragraph 3 starts with 'These forces', which refers back to something not yet mentioned. Paragraph 4 starts with 'Over time', which suggests a sequence that is not yet established.

Concluding sentence: Why this is the last line? This paragraph is the last sentence because it wraps up the main ideas. It talks about the overall importance of mountains and erosion. It gives a final thought about how mountains are part of Earth's story.

Paragraph pairs:

• Pair 1 (Paragraph 1 → Paragraph 2): Paragraph 2 connects to Paragraph 1 because it explains what happens after mountains are formed. It uses the word 'These forces' to refer back to tectonic forces. This is the Noun Pronoun Rule.
• Pair 2 (Paragraph 2 → Paragraph 3): Paragraph 3 connects to Paragraph 2 because it talks about what happens to the mountains after they are formed. It explains how erosion changes the mountains. This shows a Logical Order.
• Pair 3 (Paragraph 3 → Paragraph 4): Paragraph 4 connects to Paragraph 3 because it summarizes the importance of erosion. It shows how erosion is not just about shape but also about the history of the Earth. This is a Broader to Specific Strategy.