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. It tells us what the text will be about: how to find the age of a tree. 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 "Each ring" which is a pronoun and needs the first sentence for context. Paragraph 3 starts with "Consequently" which is a connector and needs a previous idea. Paragraph 4 starts with "However" which also needs a prior sentence.

Concluding sentence: Why this is the last line? This paragraph is the last line because it wraps up the discussion. It gives a final thought about the method of counting rings. This follows the Conclusive Words rule, as it shows a limitation of the method discussed in the text.

Paragraph pairs:

• Pair 1 (Paragraph 1 → Paragraph 2): Paragraph 2 connects to Paragraph 1 because it explains more about the rings mentioned in Paragraph 1. This follows the Broader to Specific Strategy. The first sentence gives a general idea, and the second sentence gives specific details about the rings.
• Pair 2 (Paragraph 2 → Paragraph 3): Paragraph 3 connects to Paragraph 2 because it talks about the importance of the rings. It explains what the rings can show us. This follows the Logical Order rule, as it continues the idea of the rings and adds more information.
• Pair 3 (Paragraph 3 → Paragraph 4): Paragraph 4 connects to Paragraph 3 because it gives a contrast to the information in Paragraph 3. It shows that while the rings can tell us many things, there are exceptions. This follows the Contrast rule.