A.I. Explanation:

First sentence: Why this is the first line? This paragraph is the first line because it introduces the main topic about the Celts and their influence on modern Europe. It gives a broad overview of the descendants of the Celts and mentions place names. This makes it a good starting point. Why other lines are not chosen? The other paragraphs do not qualify as the first sentence. For example, Paragraph 2 starts with "The Celts' first homeland..." which uses the definite article "the" and assumes prior knowledge. Paragraph 3 starts with "They were warriors..." which uses a pronoun "they" that refers back to the Celts. Paragraph 4 starts with "In order to scare their enemies..." which is not a general statement and does not introduce the topic.

Concluding sentence: Why this is the last line? This paragraph is the last line because it concludes the information about the Celts. It describes their battle behavior, which wraps up the discussion about them. It gives a final detail about how they fought, making it a good ending.

Paragraph pairs:

• Pair 1 (Paragraph 1 → Paragraph 2): Paragraph 2 connects with Paragraph 1 because it continues the topic of the Celts. The first paragraph talks about the descendants of the Celts, and the second paragraph gives information about where the Celts came from. This shows a logical order from general information to specific details.
• Pair 2 (Paragraph 2 → Paragraph 3): Paragraph 3 connects with Paragraph 2 because it gives more details about the Celts. After talking about their homeland, it explains what the Celts did, like being warriors and traders. This shows a logical order from where they came from to what they did.
• Pair 3 (Paragraph 3 → Paragraph 4): Paragraph 4 connects with Paragraph 3 because it continues to describe the Celtic warriors. After explaining what they did, it talks about how they prepared for battle. This shows a logical order from their actions to their battle strategies.