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 a marathon. It sets up the overall theme without going into details. It does not use any pronouns or definite articles that refer to previous information. Why other lines are not chosen? Paragraph 2 starts with 'Beginning', which is a conjunction. Paragraph 3 starts with 'It's', which uses a pronoun. Paragraph 4 starts with 'To ensure', which is not a general statement. All these reasons make them not independent.

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 gives the final important point about being ready for race day.

Paragraph pairs:

• Pair 1 (Paragraph 1 → Paragraph 2): This pair connects because Paragraph 2 gives specific details about how to prepare for the marathon. It follows the general idea of preparation from Paragraph 1. This is a Broader to Specific Strategy.
• Pair 2 (Paragraph 2 → Paragraph 3): This pair connects because Paragraph 3 talks about an important part of training, which is taking rest days. It follows logically after discussing how to build endurance. This is a Logical Order.
• Pair 3 (Paragraph 3 → Paragraph 4): This pair connects because Paragraph 4 continues the idea of preparation by discussing diet and hydration. It shows the next step in getting ready for the race. This is a Logical Order.