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 gives a broad overview of the impact of volunteering. It does not refer to any previous information. Why other lines are not chosen? The other paragraphs are not chosen because they do not stand alone. For example, Paragraph 2 starts with 'Voluntary work' which is specific and assumes prior knowledge. Paragraph 3 starts with 'It', which is a pronoun and needs context. Paragraph 4 also starts with 'It', which again needs context.

Concluding sentence: Why this is the last line? This paragraph is the last sentence because it wraps up the ideas presented. It shows the final impact of volunteering, which is to prepare people for the future. It concludes the discussion on the benefits of volunteering.

Paragraph pairs:

• Pair 1 (Paragraph 1 → Paragraph 2): Paragraph 2 connects to Paragraph 1 because it explains how volunteering affects individuals. This is a logical order where the general idea of the impact of volunteering is followed by specific benefits.
• Pair 2 (Paragraph 2 → Paragraph 3): Paragraph 3 follows Paragraph 2 because it gives a specific example of how volunteering helps. It shows a logical order from a general statement to a specific teaching.
• Pair 3 (Paragraph 3 → Paragraph 4): Paragraph 4 connects to Paragraph 3 because it continues the idea of teaching. It shows how learning to work through systems helps people in real life. This is a logical flow of ideas.