A.I. Explanation:

First sentence: Why this is the first line? This paragraph introduces the main topic of rayon production. It gives a broad overview of the different ways to make rayon. It does not use any pronouns or definite articles that refer to previous information. Why other lines are not choosen? Paragraph 2 starts with 'In this process,' which refers back to a previous idea, so it is not independent. Paragraph 3 starts with 'This is sometimes called,' which also refers back to something not yet introduced. Paragraph 4 starts with 'The solvent used for this process,' which assumes prior knowledge of the process, making it not independent.

Concluding sentence: Why this is the last line? This paragraph concludes the discussion by summarizing the dangers of the solvent used in the rayon production process. It wraps up the topic by highlighting the risks involved.

Paragraph pairs:

• Pair 1 (Paragraph 1 → Paragraph 2): Paragraph 2 explains the viscose process mentioned in Paragraph 1. This shows a logical order where the general statement about rayon production is followed by a specific explanation of one method.
• Pair 2 (Paragraph 2 → Paragraph 3): Paragraph 3 gives another name for the process described in Paragraph 2. This shows a broader to specific strategy where the specific process is followed by its alternative name.
• Pair 3 (Paragraph 3 → Paragraph 4): Paragraph 4 provides details about the solvent used in the process mentioned in Paragraph 3. This shows a logical order where the explanation of the process is followed by information about its harmful effects.