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 Box Tunnel and its history. It gives a broad overview of the subject without going into details. 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 "Unlike many tunnel rumors," which refers back to something not mentioned before. Paragraph 3 mentions a specific event, which needs context. Paragraph 4 is about a specific time and place, and Paragraph 5 talks about a view, which also needs context.

Concluding sentence: Why this is the last line? This paragraph is the last line because it wraps up the discussion about the views of the tunnel. It provides a final thought on the engineers' experience. This follows the Conclusive Words rule.

Paragraph pairs:

• Pair 1 (Paragraph 1 → Paragraph 2): Paragraph 2 connects to Paragraph 1 because it continues the topic of the Box Tunnel. It explains the nature of the rumors about the tunnel. This follows the Logical Order rule.
• Pair 2 (Paragraph 2 → Paragraph 3): Paragraph 3 connects to Paragraph 2 because it answers the question posed in Paragraph 2. It shows what happened regarding the rumor on April 9th. This follows the Question→Answer Structure rule.
• Pair 3 (Paragraph 3 → Paragraph 4): Paragraph 4 connects to Paragraph 3 because it provides details about what the engineers saw when they tested the rumor. This follows the Broader to Specific Strategy.
• Pair 4 (Paragraph 4 → Paragraph 5): Paragraph 5 connects to Paragraph 4 because it contrasts the view from the east portal with the view from the west side. This follows the Contrast rule.