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 Concorde. It gives a broad overview of when the Concorde started to carry passengers. It does not use any pronouns or definite articles that need prior context. Why other lines are not chosen? Paragraph 2 starts with "The Concorde" which uses a definite article and assumes prior knowledge. Paragraph 3 starts with "The United States" which also uses a definite article. Paragraph 4 starts with "The Concorde" which again uses a definite article. All these sentences cannot stand alone without context.

Concluding sentence: Why this is the last line? This paragraph is the last line because it concludes the story of the Concorde. It summarizes the fate of the Concorde after discussing its history. It uses conclusive language by stating the final outcome.

Paragraph pairs:

• Pair 1 (Paragraph 1 → Paragraph 2): This pair connects because Paragraph 2 gives more details about the Concorde mentioned in Paragraph 1. It follows the Broader to Specific Strategy, where the first paragraph introduces the Concorde and the second paragraph explains who operated it.
• Pair 2 (Paragraph 2 → Paragraph 3): This pair connects because it shows a contrast between the Concorde and the United States' program. It uses the Contrast rule, as it discusses two different approaches to supersonic transport.
• Pair 3 (Paragraph 3 → Paragraph 4): This pair connects because Paragraph 4 continues the story of supersonic transport by discussing the end of the Concorde's service. It follows the Logical Order rule, as it shows the timeline of events leading to the Concorde's end.