A.I. Explanation:

First sentence: Why this is the first line? This paragraph is the first line because it introduces the main topic. It tells us who is the subject (Mauro Zappaterra) and what he is doing (starting his PhD research). This is a clear introduction to the story. It does not refer to anything before it, so it stands alone. Why other lines are not chosen? The other paragraphs are not chosen because they do not meet the criteria for being independent. For example, Paragraph 2 starts with "Unfortunately," which is a conjunction. Paragraph 3 starts with "He," which is a pronoun that refers back to Zappaterra. Paragraph 4 uses "Zappaterra" but does not introduce a new idea. Paragraph 5 starts with "When he got back," which also refers back to Zappaterra.

Concluding sentence: Why this is the last line? This paragraph is the last line because it wraps up Zappaterra's story. It shows what he did after his break and learning new things. It gives a final action that connects to his research.

Paragraph pairs:

• Pair 1 (Paragraph 1 → Paragraph 2): Paragraph 2 connects with Paragraph 1 because it shows the result of Zappaterra's research. The word "Unfortunately" shows that there is a problem. This is a cause and effect relationship.
• Pair 2 (Paragraph 2 → Paragraph 3): Paragraph 3 connects with Paragraph 2 because it shows what Zappaterra did after feeling miserable. The word "finally" shows that this is a step he took after his bad feelings. This shows a logical order of events.
• Pair 3 (Paragraph 3 → Paragraph 4): Paragraph 4 connects with Paragraph 3 because it tells what Zappaterra did during his break. It gives more details about his experience. This is a broader to specific strategy.
• Pair 4 (Paragraph 4 → Paragraph 5): Paragraph 5 connects with Paragraph 4 because it shows what Zappaterra did after learning about alternative techniques. The phrase "When he got back" indicates a sequence of events. This shows chronological order.