A.I. Explanation:

First sentence: Why this is the first line? This paragraph is the first sentence because it introduces the main topic about birds' nests. It gives a broad overview of what nests are made of without going into details. This follows the rule of Topic Sentence. Why other lines are not chosen? The other paragraphs are not chosen because they do not stand alone. For example, Paragraph 2 starts with 'Big birds,' which needs context. Paragraph 3 starts with 'Small birds,' which also needs context. Paragraph 4 starts with 'Some birds,' which is not general enough. Paragraph 5 starts with 'Blackbirds,' which refers back to earlier information.

Concluding sentence: Why this is the last line? This paragraph is the last sentence because it wraps up the discussion about nests. It gives a final detail about how different birds use mud. This follows the Conclusive Words rule.

Paragraph pairs:

• Pair 1 (Paragraph 1 → Paragraph 2): Paragraph 2 connects with Paragraph 1 because it continues the topic of nests. It gives a specific example of big birds and what they use for their nests. This follows the Logical Order rule.
• Pair 2 (Paragraph 2 → Paragraph 3): Paragraph 3 connects with Paragraph 2 because it shifts from big birds to small birds. It shows a different type of nest. This follows the Topical Order rule.
• Pair 3 (Paragraph 3 → Paragraph 4): Paragraph 4 connects with Paragraph 3 because it introduces another material used in nests. It shows that not all birds use grass. This follows the Broader to Specific Strategy.
• Pair 4 (Paragraph 4 → Paragraph 5): Paragraph 5 connects with Paragraph 4 because it gives more detail about how some birds use mud. It explains what some birds do with mud. This follows the Cause and Effect Relationship rule.