A.I. Explanation:

First sentence: Why this is the first line? This paragraph is the first sentence because it introduces the main topic of physical activity and its benefits. It does not refer to any previous information. It sets the stage for the discussion about exercise. 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, 'Furthermore, regular exercise...' starts with a conjunction, so it is not independent. 'In addition to the physical benefits...' also starts with a conjunction. 'Moreover, exercise can enhance...' starts with a conjunction too. All these sentences need context from previous sentences.

Concluding sentence: Why this is the last line? This paragraph is the last sentence because it wraps up the discussion about the benefits of exercise. It gives a final point about how exercise improves life quality. This follows the rule of Conclusive Words.

Paragraph pairs:

• Pair 1 (Paragraph 1 → Paragraph 2): Paragraph 2 connects to Paragraph 1 because it continues the idea of benefits from physical activity. The word 'Furthermore' shows that it adds more information. This follows the Connector Strategy.
• Pair 2 (Paragraph 2 → Paragraph 3): Paragraph 3 connects to Paragraph 2 because it talks about another type of benefit from exercise. The phrase 'In addition to' shows that it adds more information about exercise. This follows the Connector Strategy.
• Pair 3 (Paragraph 3 → Paragraph 4): Paragraph 4 connects to Paragraph 3 because it continues to discuss the benefits of exercise. The word 'Moreover' shows that it adds another point about exercise. This follows the Connector Strategy.