A.I. Explanation:

First sentence: Why this is the first line? This paragraph is the first sentence because it introduces the main topic of workers' protection. It gives a broad overview of the situation before the 19th century. It does not use any specific details or references to previous information. Why other lines are not chosen? Paragraph 2 starts with "In the late 18th century," which gives a specific time and context, so it is not independent. Paragraph 3 uses "The first meeting," which refers to a specific event, making it not independent. Paragraph 4 starts with "Trade unions were legalized," which also refers to a specific event, so it is not independent.

Concluding sentence: Why this is the last line? This paragraph is the last sentence because it summarizes the main points about the progress of trade unions. It shows the final outcome of the workers' struggle for better conditions and protection.

Paragraph pairs:

• Pair 1 (Paragraph 1 → Paragraph 2): This pair connects because Paragraph 2 continues the story of workers. It shows how workers started to organize themselves after the poor conditions mentioned in Paragraph 1. This is a logical order of ideas.
• Pair 2 (Paragraph 2 → Paragraph 3): This pair connects because Paragraph 3 gives an example of the growth of trade unions mentioned in Paragraph 2. It shows a specific event that happened as a result of the workers' organization.
• Pair 3 (Paragraph 3 → Paragraph 4): This pair connects because Paragraph 4 continues the story of trade unions. It shows the result of the meetings and how trade unions became legal. This is a logical order of events.