A.I. Explanation:

First sentence: Why this is the first line? This paragraph is the first because it introduces the main topic of preparing for a long-distance run. It sets the stage for what is to come without needing any prior context. It gives a broad overview of the preparation process. Why other lines are not chosen? Paragraph 2 starts with 'A balanced diet,' which is specific and does not introduce the main topic. Paragraph 3 starts with 'Rest days,' which is also specific and does not introduce the topic. Paragraph 4 starts with 'On the day before the run,' which assumes prior knowledge and does not stand alone.

Concluding sentence: Why this is the last line? This paragraph is the last because it wraps up the preparation process. It gives final advice on what to do the day before the run, which is a logical conclusion to the topic.

Paragraph pairs:

• Pair 1 (Paragraph 1 → Paragraph 2): Paragraph 2 connects to Paragraph 1 because it continues the topic of preparation. The first paragraph talks about endurance, and the second paragraph explains how a balanced diet helps with that endurance.
• Pair 2 (Paragraph 2 → Paragraph 3): Paragraph 3 connects to Paragraph 2 because it continues the idea of preparation. After discussing diet, it is logical to talk about rest days, which are also important for recovery.
• Pair 3 (Paragraph 3 → Paragraph 4): Paragraph 4 connects to Paragraph 3 because it shifts focus to the day before the run. After discussing rest days, it is logical to talk about hydration and rest just before the run.