A.I. Explanation:

First sentence: Why this is the first line? This paragraph is the first sentence because it introduces the main topic about whales. It gives a broad overview of where whales live without needing other sentences for context. 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 'However,' which is a conjunction. Paragraph 3 uses 'That's why,' which connects to previous information. Paragraph 4 starts with 'When,' which also shows a connection to something before.

Concluding sentence: Why this is the last line? This paragraph is the last sentence because it wraps up the information about whales breathing. It gives a clear example of what happens when they breathe out. This follows the Summary Style rule.

Paragraph pairs:

• Pair 1 (Paragraph 1 → Paragraph 2): Paragraph 2 connects to Paragraph 1 because it uses 'However' to show a contrast. It explains that even though whales live in water, they still need to breathe air. This follows the Contrast rule.
• Pair 2 (Paragraph 2 → Paragraph 3): Paragraph 3 connects to Paragraph 2 because it explains why whales have a blowhole. The phrase 'That's why' shows a cause and effect relationship. This follows the Cause and Effect Relationship rule.
• Pair 3 (Paragraph 3 → Paragraph 4): Paragraph 4 connects to Paragraph 3 because it gives an example of what happens when whales breathe out. The word 'When' shows a logical order of events. This follows the Logical Order rule.