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 about the discovery of the ozone hole. This is a clear start to the discussion. It does not use any words that need prior 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 'Projections' which needs context. Paragraph 3 starts with 'The situation' which also needs context. Paragraph 4 starts with 'Dr. Susan Solomon' which refers to a person not introduced yet. Paragraph 5 starts with 'In a video' which needs prior information.

Concluding sentence: Why this is the last line? This paragraph is the last sentence because it wraps up the discussion. It shows how the problem was fixed and gives a sense of hope. This is a clear conclusion to the topic.

Paragraph pairs:

• Pair 1 (Paragraph 1 → Paragraph 2): Paragraph 2 connects to Paragraph 1 because it continues the topic of the ozone hole. The phrase 'Projections suggested' shows what might happen next. This is a logical order of ideas.
• Pair 2 (Paragraph 2 → Paragraph 3): Paragraph 3 connects to Paragraph 2 because it talks about the serious situation. The phrase 'The situation was dire' shows the effect of the projections. This is a cause and effect relationship.
• Pair 3 (Paragraph 3 → Paragraph 4): Paragraph 4 connects to Paragraph 3 because it explains how recovery happened. It introduces Dr. Susan Solomon's work, which is important for understanding the recovery.
• Pair 4 (Paragraph 4 → Paragraph 5): Paragraph 5 connects to Paragraph 4 because it gives more details about Dr. Solomon's work. The phrase 'In a video' shows how she shares her findings. This is a broader to specific strategy.