A.I. Explanation:

First sentence: Why this is the first line? This paragraph is the first line because it introduces the main topic of climate change in the Arctic. It uses the rule of Topic Sentence because it gives a broad overview of the subject. It does not refer to any previous information, so it stands alone. Why other lines are not choosen? Paragraph 2 starts with "Some of the clearest signs..." which makes it specific and not general. Paragraph 3 starts with "The response of the Arctic..." which also makes it specific. Paragraph 4 starts with "This is likely to affect..." which refers to something not yet mentioned, so it cannot be the first sentence.

Concluding sentence: Why this is the last line? This paragraph is the last line because it wraps up the discussion by showing the overall impact of the changes in the Arctic. It uses the rule of Summary Style, as it brings together the earlier points about climate change and its effects.

Paragraph pairs:

• Pair 1 (Paragraph 1 → Paragraph 2): Paragraph 2 connects to Paragraph 1 because it gives specific examples of the changes mentioned in Paragraph 1. This follows the Broader to Specific Strategy, where the first paragraph gives a general idea and the second paragraph provides details.
• Pair 2 (Paragraph 2 → Paragraph 3): Paragraph 3 connects to Paragraph 2 because it explains the impact of the changes mentioned in Paragraph 2. This follows the Logical Order rule, where the second paragraph gives signs of change and the third paragraph explains the response to those changes.
• Pair 3 (Paragraph 3 → Paragraph 4): Paragraph 4 connects to Paragraph 3 because it shows the wider effects of the Arctic's response to climate change. This follows the Cause and Effect Relationship rule, where the response leads to impacts beyond the Arctic.