A.I. Explanation:

First sentence: Why this is the first line? This paragraph is the first line because it introduces the main topic of bird feeding. It gives a broad overview of how many people feed birds and how common this practice is. It does not refer to any previous information, making it independent. Why other lines are not chosen? Paragraph 2 starts with a question and refers to research, so it needs context. Paragraph 3 talks about results and assumes prior knowledge. Paragraph 4 uses 'Still,' which shows it connects to something before it, so it cannot be first.

Concluding sentence: Why this is the last line? This paragraph is the last line because it raises important questions about the consequences of bird feeding. It wraps up the discussion by asking about the effects on specific species, which reflects the overarching theme of the text.

Paragraph pairs:

• Pair 1 (Paragraph 1 → Paragraph 2): The second paragraph connects to the first because it asks a question about the effects of bird feeding. This shows a logical order from the general idea of feeding birds to a specific question about its impact.
• Pair 2 (Paragraph 2 → Paragraph 3): The third paragraph follows logically because it presents preliminary results from the research mentioned in the second paragraph. This shows a clear flow from the question to the findings.
• Pair 3 (Paragraph 3 → Paragraph 4): The fourth paragraph connects to the third because it raises concerns about the results mentioned. It logically follows the findings by questioning the effects of feeding specific bird species.