A.I. Explanation:

First sentence: Why this is the first line? This paragraph is the first line because it introduces the main topic about pigeons and their ability to find their way home. It is a clear topic sentence that sets the stage for the following information. It does not refer to any previous context or use specific articles that assume prior knowledge. 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 'However,' which is a conjunction. Paragraph 3 starts with 'This skill,' which uses a pronoun that refers back to something not yet mentioned. Paragraph 4 starts with 'However,' which is also a conjunction. Therefore, they 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 about pigeons' navigation skills. It shows a new challenge they face in urban areas. The use of 'However' signals a conclusion to the previous points made about their abilities.

Paragraph pairs:

• Pair 1 (Paragraph 1 → Paragraph 2): Paragraph 2 connects with Paragraph 1 because it continues the idea of pigeons' navigation skills. It explains how their ability to find their way home includes navigating long distances. This shows a logical order from a general statement to a specific detail.
• Pair 2 (Paragraph 2 → Paragraph 3): Paragraph 3 connects with Paragraph 2 because it explains more about the skill mentioned in Paragraph 2. It provides information about why this skill is important and what it involves. This shows a broader to specific strategy.
• Pair 3 (Paragraph 3 → Paragraph 4): Paragraph 4 connects with Paragraph 3 because it introduces a new aspect of the pigeons' navigation skill. It shows a contrast by discussing how this ability can change in urban areas. The word 'However' indicates a shift in the topic.