A.I. Explanation:

First sentence: Why this is the first line? This paragraph is the first sentence because it introduces the main topic of marathon training. It gives a clear idea that you need to prepare before starting. This follows the rule of Topic Sentence. Why other lines are not chosen? The other paragraphs are not chosen because they do not stand alone. For example, Paragraph 2 starts with 'A well-structured training plan,' which needs context. Paragraph 3 starts with 'Regularly incorporating,' which also needs context. Paragraph 4 starts with 'After completing your training,' which assumes prior knowledge.

Concluding sentence: Why this is the last line? This paragraph is the last sentence because it wraps up the training process. It gives a final step to prepare for the marathon. This follows the Conclusive Words rule.

Paragraph pairs:

• Pair 1 (Paragraph 1 → Paragraph 2): Paragraph 2 connects to Paragraph 1 because it continues the idea of preparing for marathon training. This follows the Logical Order rule.
• Pair 2 (Paragraph 2 → Paragraph 3): Paragraph 3 connects to Paragraph 2 because it adds more details about what to include in your training plan. This follows the Broader to Specific Strategy.
• Pair 3 (Paragraph 3 → Paragraph 4): Paragraph 4 connects to Paragraph 3 because it talks about what to do after your training. This follows the Logical Order rule.