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 text. It gives a broad overview of the aviation industry and its importance. It does not use any specific details or references that need prior context. Why other lines are not chosen? The other paragraphs are not chosen because they do not stand alone. For example, Paragraph 2 starts with "However," which is a conjunction. Paragraph 3 uses "It" which is a pronoun that refers back to a noun. Paragraph 4 uses "The" which assumes prior knowledge of the pandemic.

Concluding sentence: Why this is the last line? This paragraph is the last sentence because it wraps up the discussion. It summarizes the main point about the need for change in the industry due to the pandemic. It reflects the overarching theme of the text.

Paragraph pairs:

• Pair 1 (Paragraph 1 → Paragraph 2): Paragraph 2 connects with Paragraph 1 because it gives more details about the aviation industry. This follows the Broader to Specific Strategy. The first sentence is general, and the second sentence provides specific examples of how the industry contributes to the economy.
• Pair 2 (Paragraph 2 → Paragraph 3): Paragraph 3 connects with Paragraph 2 because it introduces a contrast. The word "However" shows that while the industry has benefits, it also has weaknesses. This follows the Contrast rule.
• Pair 3 (Paragraph 3 → Paragraph 4): Paragraph 4 connects with Paragraph 3 because it explains the consequences of the vulnerabilities mentioned in Paragraph 3. This follows the Cause and Effect Relationship rule. The pandemic's impact is a direct result of the industry's vulnerabilities.