A.I. Explanation:

First sentence: Why this is the first line? This paragraph is the first because it introduces Karl Marx, who is the main topic. It gives a broad overview of his importance and work. It does not refer to any previous information, so it stands alone. Why other lines are not chosen? Paragraph 2 starts with "In this landmark account," which needs context. Paragraph 3 starts with "Historically," which suggests it follows another idea. Paragraph 4 starts with "Welfare has a special political meaning," which also needs prior context.

Concluding sentence: Why this is the last line? This paragraph is the last because it wraps up the discussion about welfare. It compares the situation in the United States with other regions, giving a clear conclusion to the topic.

Paragraph pairs:

• Pair 1 (Paragraph 1 → Paragraph 2): Paragraph 2 connects to Paragraph 1 because it continues the discussion about social issues. The phrase "In this landmark account" shows that it is talking about a specific work related to the topics Marx discussed.
• Pair 2 (Paragraph 2 → Paragraph 3): Paragraph 3 connects to Paragraph 2 because it discusses political issues. The word "Historically" shows that it is looking back at how political systems have affected society, linking it to the previous discussion about the poor.
• Pair 3 (Paragraph 3 → Paragraph 4): Paragraph 4 connects to Paragraph 3 because it continues the theme of political issues. The discussion about welfare in the United States relates to the political autonomy mentioned in Paragraph 3.