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 clearly states that the brain is the most extraordinary human feature. This follows the rule of Topic Sentence. Why other lines are not chosen? The other paragraphs do not qualify as the first sentence. For example, Paragraph 2 starts with 'The relative size...' which uses the definite article 'the' and refers to a specific feature, so it cannot stand alone. Paragraph 3 starts with 'To be more specific...' which is a transitional phrase. Paragraph 4 starts with 'In contrast...' which also indicates a continuation of thought.

Concluding sentence: Why this is the last line? This paragraph is the last sentence because it wraps up the discussion about the human brain by comparing it to other mammals. It uses the word 'In contrast,' which signals a conclusion. This follows the Conclusive Words rule.

Paragraph pairs:

• Pair 1 (Paragraph 1 → Paragraph 2): Paragraph 2 connects to Paragraph 1 because it gives more information about the brain. This follows the Broader to Specific Strategy. The first sentence introduces the brain, and the second sentence explains its size and capacity.
• Pair 2 (Paragraph 2 → Paragraph 3): Paragraph 3 connects to Paragraph 2 because it gives a specific detail about the size of the human brain. This follows the General to Specific Strategy. The second sentence talks about the brain's capacity, and the third sentence gives a specific ratio.
• Pair 3 (Paragraph 3 → Paragraph 4): Paragraph 4 connects to Paragraph 3 because it contrasts the human brain's ratio with that of other mammals. This follows the Contrast Strategy. The third sentence gives the human ratio, and the fourth sentence shows how it is different from other mammals.