A.I. Explanation:

First sentence: Why this is the first line? This paragraph is the first sentence because it introduces the main topic. It tells us who Steven Witherly is and what he studies. This is a clear topic sentence. It does not need any other sentence for context. Why other lines are not chosen? The other paragraphs are not chosen because they do not stand alone. For example, Paragraph 2 starts with "According to Witherly," which needs context. Paragraph 3 starts with "First," which shows it is not the first. Paragraph 4 starts with "The second factor," which also needs earlier information.

Concluding sentence: Why this is the last line? This paragraph is the last sentence because it gives the second factor that makes food pleasurable. It wraps up the ideas from the previous paragraphs. It completes the explanation of the two factors.

Paragraph pairs:

• Pair 1 (Paragraph 1 → Paragraph 2): Paragraph 2 connects to Paragraph 1 because it uses the phrase "According to Witherly." This shows that it continues the idea from the first paragraph. It gives more information about what Witherly says.
• Pair 2 (Paragraph 2 → Paragraph 3): Paragraph 3 connects to Paragraph 2 because it starts with "First." This shows it is giving the first factor of the two mentioned in Paragraph 2. It follows a logical order.
• Pair 3 (Paragraph 3 → Paragraph 4): Paragraph 4 connects to Paragraph 3 because it uses the phrase "The second factor." This shows it is giving the second factor after explaining the first one. It follows the logical order of ideas.