A.I. Explanation:

First sentence: Why this is the first line? This paragraph is the first line because it introduces the main topic. It tells us about the German invasion of Poland, which is a key event. This is a broad overview of the start of the Second World War. Why other lines are not chosen? The other paragraphs are not chosen because they do not stand alone. For example, Paragraph 2 starts with 'In the beginning,' which is a phrase that needs context. Paragraph 3 starts with 'But,' which is a conjunction. Paragraph 4 uses 'They,' which refers back to something not yet mentioned. Paragraph 5 starts with 'Meanwhile,' which also needs prior context.

Concluding sentence: Why this is the last line? This paragraph is the last line because it wraps up the discussion. It shows a new topic about atomic energy, which is different from the previous paragraphs. It gives a broader view of the world after discussing Poland.

Paragraph pairs:

• Pair 1 (Paragraph 1 → Paragraph 2): Paragraph 2 connects with Paragraph 1 because it continues the story. The first paragraph talks about the invasion, and the second talks about the hope of Britain and France. This shows a logical order of events.
• Pair 2 (Paragraph 2 → Paragraph 3): Paragraph 3 connects with Paragraph 2 because it shows the contrast. The second paragraph talks about hope, and the third shows that this hope was not true. This is a cause and effect relationship.
• Pair 3 (Paragraph 3 → Paragraph 4): Paragraph 4 connects with Paragraph 3 because it explains why the Polish forces could not defend. It gives more details about the problems they faced. This is a broader to specific strategy.
• Pair 4 (Paragraph 4 → Paragraph 5): Paragraph 5 connects with Paragraph 4 because it shifts the focus to the world outside of Poland. It shows what was happening globally while Poland was struggling. This is a topical order.