A.I. Explanation:

First sentence: Why this is the first line? This paragraph is the first sentence because it introduces the main topic of choosing a marathon. It sets the stage for what comes next. It does not refer to any previous information, making it independent. 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 "It's crucial" which is a pronoun and needs context. Paragraph 3 starts with "Once you've chosen" which refers back to a previous idea. Paragraph 4 starts with "Finally" which shows it is not the first idea.

Concluding sentence: Why this is the last line? This paragraph is the last sentence because it wraps up the ideas about marathon training. The word "Finally" signals that this is the conclusion of the steps. It summarizes the overall theme of preparing for a marathon.

Paragraph pairs:

• Pair 1 (Paragraph 1 → Paragraph 2): Paragraph 2 connects with Paragraph 1 because it continues the idea of preparing for a marathon. The phrase "It's crucial" shows the importance of the next step after choosing a marathon. This follows the Logical Order rule.
• Pair 2 (Paragraph 2 → Paragraph 3): Paragraph 3 connects with Paragraph 2 because it talks about the next step after selecting a training plan. The phrase "Once you've chosen your marathon" shows a clear sequence of actions. This follows the Chronological Order rule.
• Pair 3 (Paragraph 3 → Paragraph 4): Paragraph 4 connects with Paragraph 3 because it adds another important part of training after setting goals. The word "Finally" shows that this is the last step in the process. This follows the Logical Order rule.