A.I. Explanation:

First sentence: Why this is the first line? This paragraph is the first because it introduces the main topic of economic prosperity in Western Europe. It gives a broad overview of the economic situation in Britain, France, and Germany without needing prior context. It sets the stage for the discussion about the Industrial Revolution. Why other lines are not chosen? Paragraph 2 starts with "At the turn of the 19th century," which suggests it needs context from earlier sentences. Paragraph 3 begins with "Even two decades later," which also needs context. Paragraph 4 starts with "It would be a mistake to call the other two countries underdeveloped," which refers back to previous ideas and does not stand alone.

Concluding sentence: Why this is the last line? This paragraph is the last because it wraps up the discussion. It contrasts the cultural achievements of the other countries with Britain's economic situation. It provides a final thought on the topic, summarizing the main points.

Paragraph pairs:

• Pair 1 (Paragraph 1 → Paragraph 2): The second paragraph connects to the first because it continues the discussion about Britain's economy. The phrase "At the turn of the 19th century, however," shows a change in the situation, linking the two ideas.
• Pair 2 (Paragraph 2 → Paragraph 3): The third paragraph follows logically because it talks about the situation two decades later. The phrase "Even two decades later" shows a time connection, continuing the story of Britain's industrial development.
• Pair 3 (Paragraph 3 → Paragraph 4): The fourth paragraph connects because it discusses the other two countries in relation to Britain. The phrase "It would be a mistake to call the other two countries underdeveloped" shows a contrast to the previous paragraph, linking the ideas.