A.I. Explanation:

First sentence: Why this is the first line? This paragraph is the first line because it introduces the main topic. It talks about Airbnb and when it started. It does not need other sentences to understand it. It does not use words that need prior context. Why other lines are not chosen? Paragraph 2 starts with 'People' and needs context from the first paragraph. Paragraph 3 starts with 'Fast forward' which shows it is not independent. Paragraph 4 starts with 'It is' which refers back to Airbnb, so it is not independent.

Concluding sentence: Why this is the last line? This paragraph is the last line because it wraps up the story of Airbnb. It shows how successful the company has become. It gives a final thought about its place in the sharing economy.

Paragraph pairs:

• Pair 1 (Paragraph 1 → Paragraph 2): Paragraph 2 connects to Paragraph 1 because it explains what Airbnb's dream is. This is a Broader to Specific Strategy. The first paragraph gives a general idea, and the second paragraph gives more details.
• Pair 2 (Paragraph 2 → Paragraph 3): Paragraph 3 connects to Paragraph 2 because it talks about how Airbnb is important for millennials. This is a Logical Order. The second paragraph gives an example of Airbnb, and the third paragraph explains its impact.
• Pair 3 (Paragraph 3 → Paragraph 4): Paragraph 4 connects to Paragraph 3 because it shows how Airbnb has grown over time. This is a Chronological Order. The third paragraph talks about millennials, and the fourth paragraph gives a time reference to 2016.