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 Stone Age. It gives a broad overview of the time period without going into details. 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 'This period', which uses a pronoun and needs context. Paragraph 3 starts with 'During the first period', which also needs context. Paragraph 4 starts with 'As a result of the Ice Age', which refers to something that is not introduced yet.

Concluding sentence: Why this is the last line? This paragraph is the last sentence because it wraps up the discussion about the Stone Age and its effects. It shows the result of the Ice Age and how it changed people's lives. This follows the rule of Conclusive Words.

Paragraph pairs:

• Pair 1 (Paragraph 1 → Paragraph 2): Paragraph 2 connects to Paragraph 1 because it continues to explain the Stone Age. It uses the phrase 'This period', which refers back to the Stone Age mentioned in Paragraph 1. This follows the Noun Pronoun Rule.
• Pair 2 (Paragraph 2 → Paragraph 3): Paragraph 3 connects to Paragraph 2 because it gives more details about the first part of the Stone Age. It explains what happened during the first period. This follows the Broader to Specific Strategy.
• Pair 3 (Paragraph 3 → Paragraph 4): Paragraph 4 connects to Paragraph 3 because it explains the effects of the Ice Age on people during the Palaeolithic Age. It shows how the developments in Paragraph 3 led to changes in lifestyle. This follows the Cause and Effect Relationship.