A.I. Explanation:

First sentence: Why this is the first line? This paragraph is the first sentence because it introduces the main topic about the extinct animal. It does not need another sentence for context. It gives a broad overview of the subject. Why other lines are not chosen? Paragraph 2 starts with 'Researchers think', which needs context. Paragraph 3 starts with 'The findings', which also needs context. Paragraph 4 starts with 'The fossil', which assumes prior knowledge. Paragraph 5 starts with 'It then', which refers back to something not yet introduced.

Concluding sentence: Why this is the last line? This paragraph is the last sentence because it wraps up the story of the fossil. It gives closure to the information presented in the previous paragraphs.

Paragraph pairs:

• Pair 1 (Paragraph 1 → Paragraph 2): This pair connects because Paragraph 2 explains more about the extinct animal described in Paragraph 1. It uses the 'Broader to Specific Strategy' as it gives specific information about the animal's relation to the river dolphin.
• Pair 2 (Paragraph 2 → Paragraph 3): This pair connects because Paragraph 3 presents the results of the research mentioned in Paragraph 2. It follows a 'Logical Order' as it shows the outcome of the research.
• Pair 3 (Paragraph 3 → Paragraph 4): This pair connects because Paragraph 4 gives background information about the fossil related to the findings in Paragraph 3. It uses the 'Topical Order' as it continues the discussion about the fossil.
• Pair 4 (Paragraph 4 → Paragraph 5): This pair connects because Paragraph 5 continues the story of the fossil from Paragraph 4. It uses 'Chronological Order' as it describes what happened to the fossil after its discovery.