A.I. Explanation:

First sentence: Why this is the first line? This paragraph is the first sentence because it introduces the main topic. It talks about the aim of European politicians after the Second World War. This is a broad overview of the topic. It does not use any pronouns or definite articles that need prior context. Why other lines are not chosen? Paragraph 2 starts with "The European Coal and Steel Community" which uses the definite article "the" and assumes prior knowledge. Paragraph 3 starts with "In 1957" which gives a specific time and does not introduce the topic. Paragraph 4 starts with "This period, however," which uses a pronoun and needs context from earlier sentences.

Concluding sentence: Why this is the last line? This paragraph is the last sentence because it wraps up the discussion. It introduces a new idea about the Cold War that contrasts with the earlier ideas of cooperation. It shows the outcome of the earlier efforts and concludes the topic.

Paragraph pairs:

• Pair 1 (Paragraph 1 → Paragraph 2): Paragraph 2 connects with Paragraph 1 because it continues the idea of building peace. The first paragraph talks about the aim of creating the European Union, and the second paragraph gives an example of this aim with the European Coal and Steel Community. This shows a logical order from a general idea to a specific example.
• Pair 2 (Paragraph 2 → Paragraph 3): Paragraph 3 connects with Paragraph 2 because it continues the topic of European cooperation. The second paragraph talks about the first step, and the third paragraph explains the next step in this process. This shows a logical order of events.
• Pair 3 (Paragraph 3 → Paragraph 4): Paragraph 4 connects with Paragraph 3 because it discusses the time after the Treaty of Rome. The third paragraph talks about cooperation, and the fourth paragraph introduces a contrasting idea of the Cold War. This shows a contrast between cooperation and division.