A.I. Explanation:

First sentence: Why this is the first line? This paragraph is the first sentence because it introduces the main topic about bird nests. It gives a broad overview of what most bird nests are made of. 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 'Though' which is a conjunction. Paragraph 3 uses 'Some of the strangest nests' which is not a general statement. Paragraph 4 starts with 'The common swift' which uses a definite article. Paragraph 5 starts with 'Some tropical swifts' which is also not a general statement.

Concluding sentence: Why this is the last line? This paragraph is the last sentence because it wraps up the information about swift nests. It gives a final detail about how some swifts make their nests. This follows the Conclusive Words rule.

Paragraph pairs:

• Pair 1 (Paragraph 1 → Paragraph 2): Paragraph 2 connects with Paragraph 1 because it adds more information about different types of nests. This follows the Broader to Specific Strategy.
• Pair 2 (Paragraph 2 → Paragraph 3): Paragraph 3 connects with Paragraph 2 because it introduces another type of nest. This follows the Logical Order rule.
• Pair 3 (Paragraph 3 → Paragraph 4): Paragraph 4 connects with Paragraph 3 because it gives an example of the nests made by swifts. This follows the Topic Example rule.
• Pair 4 (Paragraph 4 → Paragraph 5): Paragraph 5 connects with Paragraph 4 because it talks about another type of swift nest. This follows the Logical Order rule.