First sentence: Why this is the first line? This paragraph is the first because it introduces the topic of railways. It gives a general idea about railways being a good invention and mentions wooden railways. This fits the rule of Topic Sentence because it sets up the main topic without going into details. Why other lines are not chosen? Paragraph 2 starts with "The" which makes it dependent on prior information. Paragraph 3 starts with "Later on," which shows it is not independent. Paragraph 4 starts with "With the industrial development," which also shows it is not independent.

Concluding sentence: Why this is the last line? This paragraph is the last because it wraps up the topic of railways. It gives a final detail about the invention of steel railways, which concludes the discussion on the development of railways.

Paragraph pairs:

• Pair 1 (Paragraph 1 → Paragraph 2): Paragraph 2 connects to Paragraph 1 because it continues the idea of railways. It uses the Connector strategy as it explains a benefit of railways after stating they are a good invention.
• Pair 2 (Paragraph 2 → Paragraph 3): Paragraph 3 connects to Paragraph 2 because it shows a development in railways. It follows the Logical Order rule as it explains what happened after railways were introduced.
• Pair 3 (Paragraph 3 → Paragraph 4): Paragraph 4 connects to Paragraph 3 because it gives more information about the development of railways. It follows the Broader to Specific Strategy as it provides a specific example of railway development.