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, which is the pencil. It gives a broad overview of what the text will discuss. 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 "Its" which is a pronoun and needs context. Paragraph 3 starts with "Initially" which is a transitional word. Paragraph 4 starts with "As" which is also a conjunction. All these words show that these sentences need more information to make sense.

Concluding sentence: Why this is the last line? This paragraph is the last line because it wraps up the discussion about the pencil's evolution. It shows the final result of the changes made to the pencil. This follows the rule of Conclusive Words.

Paragraph pairs:

• Pair 1 (Paragraph 1 → Paragraph 2): Paragraph 2 connects to Paragraph 1 because it gives more specific information about the pencil's history. This follows the Broader to Specific Strategy.
• Pair 2 (Paragraph 2 → Paragraph 3): Paragraph 3 connects to Paragraph 2 because it explains what happened after graphite was discovered. This shows a logical order of events.
• Pair 3 (Paragraph 3 → Paragraph 4): Paragraph 4 connects to Paragraph 3 because it continues the story of how the pencil changed over time. This follows the Logical Order strategy.