A.I. Explanation:

First sentence: Why this is the first line? This paragraph is the first sentence because it introduces the main topic of the text. It talks about the importance of physical activity for both body and mind. This is a broad overview of what the text will discuss. Why other lines are not chosen? Paragraph 2 starts with "When we engage..." which is a dependent clause and needs more context. Paragraph 3 starts with "Many people underestimate..." which refers to a previous idea. Paragraph 4 starts with "Additionally..." which shows it is adding to something already mentioned.

Concluding sentence: Why this is the last line? This paragraph is the last sentence because it summarizes the benefits of regular exercise. It wraps up the discussion by showing how exercise can help with mental health issues.

Paragraph pairs:

• Pair 1 (Paragraph 1 → Paragraph 2): Paragraph 2 connects to Paragraph 1 because it explains how physical activity helps mental well-being. The phrase "When we engage in physical activities" shows a direct link to the topic of physical activity.
• Pair 2 (Paragraph 2 → Paragraph 3): Paragraph 3 follows Paragraph 2 because it discusses the impact of physical activity. It shows that many people do not see how staying active can help their mental health.
• Pair 3 (Paragraph 3 → Paragraph 4): Paragraph 4 connects to Paragraph 3 because it gives more details about how exercise can help. The word "Additionally" shows that it adds more information about the benefits of exercise.