A.I. Explanation:

First sentence: Why this is the first line? This paragraph is the first sentence because it introduces a specific event that happened in the past. It gives a clear time and place, which helps the reader understand the context. This follows the rule of Chronological or Logical Context-Setting. Why other lines are not chosen? The other paragraphs are not chosen because they do not stand alone. For example, Paragraph 2 starts with "Today," which connects it to a time that is not the beginning. Paragraph 3 uses "The US Interagency Fire Center" which assumes prior knowledge. Paragraph 4 starts with "Other wildfire experts" which also assumes previous context.

Concluding sentence: Why this is the last line? This paragraph is the last sentence because it wraps up the discussion about megafires. It gives a broader view of what a megafire means, which helps to conclude the topic. This follows the rule of Summary Style.

Paragraph pairs:

• Pair 1 (Paragraph 1 → Paragraph 2): Paragraph 2 connects to Paragraph 1 because it talks about the same place, Yellowstone. The word "Today" shows a shift in time from the past event in Paragraph 1 to the present. This follows the rule of Logical Order.
• Pair 2 (Paragraph 2 → Paragraph 3): Paragraph 3 connects to Paragraph 2 because it explains what a megafire is. The phrase "defines a megafire" shows that it gives more details about the topic introduced in Paragraph 2. This follows the rule of Broader to Specific Strategy.
• Pair 3 (Paragraph 3 → Paragraph 4): Paragraph 4 connects to Paragraph 3 because it adds more information about megafires. It shows that there is more than one way to define a megafire. This follows the rule of Logical Order.