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 the marathon. It shows the start of the preparation process. It does not refer to any previous information, so it stands alone. This follows the rule of Topic Sentence. Why other lines are not chosen? Paragraph 2 starts with "Initially," which is a transitional word, so it cannot be first. Paragraph 3 starts with "Once," which also shows a sequence and cannot be first. Paragraph 4 does not stand alone because it refers to previous steps in training.

Concluding sentence: Why this is the last line? This paragraph is the last sentence because it wraps up the preparation process. It uses the phrase "The final step" which shows it is the conclusion of the training. This follows the Conclusive Words rule.

Paragraph pairs:

• Pair 1 (Paragraph 1 → Paragraph 2): Paragraph 2 connects with Paragraph 1 because it continues the idea of preparation. The word "Initially" shows that this is the first action after registering. This follows the Logical Order rule.
• Pair 2 (Paragraph 2 → Paragraph 3): Paragraph 3 connects with Paragraph 2 because it shows the next step after researching. The word "Once" indicates that this action happens after the research. This follows the Chronological Order rule.
• Pair 3 (Paragraph 3 → Paragraph 4): Paragraph 4 connects with Paragraph 3 because it shows the last step in the preparation. The phrase "The final step" indicates that this is the last action after finding accommodation. This follows the Logical Order rule.