A.I. Explanation:

First sentence: Why this is the first line? This paragraph is the first line because it introduces the main topic of the text. It gives a broad overview of the history of the "sky island" mountains. It does not refer to any previous information. Why other lines are not chosen? Paragraph 2 starts with "That's because" which is a conjunction, so it cannot be first. Paragraph 3 starts with "These" which is a pronoun and needs context. Paragraph 4 starts with "They" which is also a pronoun. Paragraph 5 starts with "The" which is a definite article and assumes prior knowledge.

Concluding sentence: Why this is the last line? This paragraph is the last line because it summarizes the main topic. It gives specific details about the sunbirds and wraps up the information about them.

Paragraph pairs:

• Pair 1 (Paragraph 1 → Paragraph 2): Paragraph 2 connects to Paragraph 1 because it explains why the soundtrack has not changed. The phrase "That's because" shows a cause and effect relationship.
• Pair 2 (Paragraph 2 → Paragraph 3): Paragraph 3 connects to Paragraph 2 because it identifies the birds mentioned. The phrase "These colorful, tiny, nectar-feeding birds" refers back to the birds in Paragraph 2, showing a Noun Pronoun Rule.
• Pair 3 (Paragraph 3 → Paragraph 4): Paragraph 4 connects to Paragraph 3 because it gives more information about sunbirds. The word "They" refers back to the sunbirds, showing a Noun Pronoun Rule.
• Pair 4 (Paragraph 4 → Paragraph 5): Paragraph 5 connects to Paragraph 4 because it gives specific information about a type of sunbird. The phrase "The most famous eastern double-collared sunbirds" shows a Broader to Specific Strategy.