A.I. Explanation:

First sentence: Why this is the first line? This paragraph is the first line because it introduces the main topic. It talks about the American mink and its history in Iceland. This is an overview of the subject. It does not use any words that need prior context. Why other lines are not chosen? Paragraph 2 starts with "The ecosystem" which is specific and needs context. Paragraph 3 starts with "Direct competition" which also needs context. Paragraph 4 starts with "Iceland is therefore" which shows a conclusion and needs prior information.

Concluding sentence: Why this is the last line? This paragraph is the last line because it wraps up the discussion. It gives a conclusion about why Iceland is a good place to study the mink. It summarizes the main points made in the earlier paragraphs.

Paragraph pairs:

• Pair 1 (Paragraph 1 → Paragraph 2): Paragraph 2 connects to Paragraph 1 because it continues the discussion about the mink. It explains the environment where the mink lives. This shows a logical order of ideas.
• Pair 2 (Paragraph 2 → Paragraph 3): Paragraph 3 connects to Paragraph 2 because it talks about the relationship between the mink and the arctic fox. It explains the competition in the ecosystem. This shows a logical order of ideas.
• Pair 3 (Paragraph 3 → Paragraph 4): Paragraph 4 connects to Paragraph 3 because it concludes the discussion about the mink and the arctic fox. It shows why studying the mink in Iceland is important. This shows a logical order of ideas.