First sentence: Why this is the first line? This paragraph is the first sentence because it introduces the main topic. It tells us about Notre-Dame Cathedral and its importance as a masterpiece of Gothic architecture. This is a general statement that does not need other sentences for context. It does not start with a conjunction or use pronouns. Why other lines are not chosen? Paragraph 2 starts with 'This' which is a pronoun, so it cannot be independent. Paragraph 3 starts with 'The' which is a definite article and assumes prior knowledge. Paragraph 4 starts with 'It' which is also a pronoun. All these reasons make them not independent.

Concluding sentence: Why this is the last line? This paragraph is the last sentence because it wraps up the main ideas. It summarizes the importance of Notre-Dame Cathedral as a symbol of France. The phrase 'has been a symbol' indicates a conclusion to the discussion about the cathedral.

Paragraph pairs:

• Pair 1 (Paragraph 1 → Paragraph 2): Paragraph 2 connects with Paragraph 1 because it continues the topic of Notre-Dame Cathedral. It uses the phrase 'It has also witnessed' which refers back to the cathedral. This shows a logical order from describing the cathedral to mentioning its historical events.
• Pair 2 (Paragraph 2 → Paragraph 3): Paragraph 3 connects with Paragraph 2 because it shifts focus from historical events to the beauty of the cathedral. The phrase 'The cathedral's stunning stained glass windows' shows a broader to specific strategy, moving from general history to specific features.
• Pair 3 (Paragraph 3 → Paragraph 4): Paragraph 4 connects with Paragraph 3 because it summarizes the importance of the cathedral. The phrase 'This impressive architectural marvel' refers back to the cathedral, showing a logical order from its beauty to its symbolic status.