A.I. Explanation:

First sentence: Why this is the first line? This paragraph is the first sentence because it introduces the main topic of paper towels. It gives a broad overview of what paper towels are and their use. It does not refer to any previous information. Why other lines are not chosen? The other paragraphs are not chosen as the first sentence because: 1. Paragraph 2 starts with 'They', which is a pronoun and needs context. 2. Paragraph 3 starts with 'Consequently', which is a connector and shows a result, not an introduction. 3. Paragraph 4 starts with 'However', which is also a connector and shows contrast, not an introduction.

Concluding sentence: Why this is the last line? This paragraph is the last sentence because it wraps up the discussion about paper towels. It summarizes the benefits after talking about their impact. It gives a clear conclusion to the topic.

Paragraph pairs:

• Pair 1 (Paragraph 1 → Paragraph 2): Paragraph 2 connects with Paragraph 1 because it uses the pronoun 'They' to refer back to 'Paper towels'. This shows a clear link between the two sentences.
• Pair 2 (Paragraph 2 → Paragraph 3): Paragraph 3 connects with Paragraph 2 because it uses 'Consequently', which shows a cause and effect relationship. The production of paper towels is a result of what they are made from.
• Pair 3 (Paragraph 3 → Paragraph 4): Paragraph 4 connects with Paragraph 3 because it starts with 'However', which shows contrast. It talks about the benefits of paper towels after discussing their environmental impact.