First sentence: Why this is the first line? This paragraph is the first line because it introduces the main topic of the text. It talks about how cities are growing quickly after a long time of slow growth. This is an overview of the main idea. It does not refer to any previous information, so it is independent. Why other lines are not choosen? The other paragraphs are not chosen because they do not meet the criteria for being the first sentence. For example, Paragraph 2 starts with 'The world population...' which is not a general statement. Paragraph 3 starts with 'To give only one example...' which is not independent. Paragraph 4 starts with 'There is no reason...' which assumes prior knowledge.

Concluding sentence: Why this is the last line? This paragraph is the last line because it wraps up the main idea of the text. It suggests that the fast growth of cities will continue. This is a conclusion that reflects the overall theme of the text.

Paragraph pairs:

• Pair 1 (Paragraph 1 → Paragraph 2): Paragraph 2 connects with Paragraph 1 because it continues the idea of rapid growth. The phrase 'the cities are suddenly racing off' leads to the statistics about population growth. This shows a logical order of ideas.
• Pair 2 (Paragraph 2 → Paragraph 3): Paragraph 3 connects with Paragraph 2 because it gives a specific example of the growth mentioned in Paragraph 2. The phrase 'to give only one example' shows that it is explaining the previous point. This is a broader to specific strategy.
• Pair 3 (Paragraph 3 → Paragraph 4): Paragraph 4 connects with Paragraph 3 because it talks about the future of this growth. The idea that Athens is growing quickly leads to the conclusion that this growth will continue. This shows a cause and effect relationship.