A.I. Explanation:

First sentence: Why this is the first line? This paragraph is the first sentence because it introduces the main topic of helicopters. It gives a general idea about the history of helicopters. It does not use any words that need prior context. This makes it a good opening 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 "The first powered helicopter..." which needs context from earlier sentences. Paragraph 3 starts with "It rose..." which uses a pronoun that refers back to something else. Paragraph 4 starts with "And the first..." which is a conjunction and needs a previous sentence for meaning.

Concluding sentence: Why this is the last line? This paragraph is the last sentence because it wraps up the history of helicopters. It shows the final important step in the development of helicopters. It gives a conclusion to the topic.

Paragraph pairs:

• Pair 1 (Paragraph 1 → Paragraph 2): This pair connects because Paragraph 2 gives a specific example of a helicopter after the general idea in Paragraph 1. This follows the Broader to Specific Strategy.
• Pair 2 (Paragraph 2 → Paragraph 3): This pair connects because Paragraph 3 gives details about the helicopter mentioned in Paragraph 2. This follows the Logical Order strategy, as it explains what happened after the design.
• Pair 3 (Paragraph 3 → Paragraph 4): This pair connects because Paragraph 4 talks about the next important helicopter after the one in Paragraph 3. This follows the Chronological Order strategy, as it shows the timeline of helicopter development.