A.I. Explanation:

First sentence: Why this is the first line? This paragraph is the first sentence because it introduces the main topic of balance in climbing. It is a general statement that does not need other sentences for context. It does not start with a conjunction or use pronouns. Why other lines are not chosen? Paragraph 2 starts with 'Without' which makes it dependent on prior context. Paragraph 3 starts with 'Besides' which is a conjunction. Paragraph 4 starts with 'Therefore' which also indicates it is dependent on previous information.

Concluding sentence: Why this is the last line? This paragraph is the last sentence because it wraps up the ideas about balance and core strength. It shows the result of the previous points and concludes the discussion.

Paragraph pairs:

• Pair 1 (Paragraph 1 → Paragraph 2): Paragraph 2 connects to Paragraph 1 because it explains what happens without balance. This shows a cause and effect relationship.
• Pair 2 (Paragraph 2 → Paragraph 3): Paragraph 3 connects to Paragraph 2 because it adds more information about balance. It shows that core strength is also important, which supports the idea of balance.
• Pair 3 (Paragraph 3 → Paragraph 4): Paragraph 4 connects to Paragraph 3 because it explains the result of increasing core strength. It shows a logical order where improving core strength leads to better balance.