A.I. Explanation:

First sentence: Why this is the first line? This paragraph is the first sentence because it introduces the main topic of the text. It gives a broad overview of Darwin's theory, which is the main subject. 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 'It', which is a pronoun and needs context. Paragraph 3 starts with 'These changes', which also needs prior information. Paragraph 4 starts with 'Consequently', which is a transitional word and shows it is not independent.

Concluding sentence: Why this is the last line? This paragraph is the last sentence because it wraps up the ideas presented. It shows the result of adaptation, which is the conclusion of the discussion about evolution.

Paragraph pairs:

• Pair 1 (Paragraph 1 → Paragraph 2): Paragraph 2 connects to Paragraph 1 because it explains what Darwin's theory argues. This follows the Logical Order rule, as it continues the idea of evolution.
• Pair 2 (Paragraph 2 → Paragraph 3): Paragraph 3 connects to Paragraph 2 because it describes the changes mentioned in Paragraph 2. This follows the Broader to Specific Strategy, as it gives more detail about the changes.
• Pair 3 (Paragraph 3 → Paragraph 4): Paragraph 4 connects to Paragraph 3 because it explains the result of the changes. This follows the Cause and Effect Relationship rule, as it shows what happens when organisms adapt.