A.I. Explanation:

First sentence: Why this is the first line? This paragraph is the first sentence because it introduces the main topic of preparing for training. It uses the rule of Topic Sentence because it gives a clear idea about what is important before starting training. It does not refer to any previous information, making it independent. Why other lines are not chosen? The other paragraphs are not chosen because they do not meet the criteria for being independent. For example, Paragraph 2 starts with 'Integrating,' which is not a general statement. Paragraph 3 starts with 'A balanced diet,' which assumes prior knowledge of diet. Paragraph 4 starts with 'Finally,' which shows it is not the first sentence.

Concluding sentence: Why this is the last line? This paragraph is the last sentence because it wraps up the ideas about preparing for a marathon. It uses the rule of Conclusive Words with 'Finally,' showing it is the end of the discussion. It also summarizes the importance of motivation and focus after all the preparation steps.

Paragraph pairs:

• Pair 1 (Paragraph 1 → Paragraph 2): Paragraph 2 connects with Paragraph 1 because it continues the idea of preparing for training. This follows the Logical Order rule, as after a medical check-up, the next step is to start training with long runs.
• Pair 2 (Paragraph 2 → Paragraph 3): Paragraph 3 connects with Paragraph 2 because it talks about another important part of training, which is diet. This follows the Broader to Specific Strategy, as it goes from the specific action of running to the broader topic of nutrition.
• Pair 3 (Paragraph 3 → Paragraph 4): Paragraph 4 connects with Paragraph 3 because it discusses the next step after nutrition, which is setting goals. This follows the Logical Order rule, as after preparing your body with diet, you need to focus on your goals.