A.I. Explanation:

First sentence: Why this is the first line? This paragraph is the first because it gives a general idea about precious stones. It introduces the main topic of the text. It does not refer to any previous information. This follows the rule of Topic Sentence. Why other lines are not chosen? The other paragraphs are not independent. For example, Paragraph 2 starts with 'Amber' which is a specific subject and assumes prior knowledge. Paragraph 3 starts with 'It' which is a pronoun that refers back to something else. Paragraph 4 starts with 'Many' which is also not general enough to stand alone.

Concluding sentence: Why this is the last line? This paragraph is the last because it wraps up the information about amber. It gives a final detail about what is found in amber. This follows the Conclusive Words rule.

Paragraph pairs:

• Pair 1 (Paragraph 1 → Paragraph 2): Paragraph 2 connects to Paragraph 1 because it gives a specific example of one type of precious stone, amber. This follows the Broader to Specific Strategy.
• Pair 2 (Paragraph 2 → Paragraph 3): Paragraph 3 connects to Paragraph 2 because it explains how amber is formed. This follows the Logical Order rule, as it continues the explanation about amber.
• Pair 3 (Paragraph 3 → Paragraph 4): Paragraph 4 connects to Paragraph 3 because it gives more information about amber. It shows what else can be found in amber. This follows the Topic Example rule.