A.I. Explanation:

First sentence: Why this is the first line? This paragraph is the first line because it introduces the main topic about Afghanistan. It gives a broad overview of a significant feature of the country, which is the Hindu Kush mountain range. This follows the rule of Topic Sentence. Why other lines are not chosen? The other paragraphs are not chosen because they do not stand alone. For example, Paragraph 2 starts with 'The overland route,' which needs context. Paragraph 3 starts with 'It is one of the world's poorest countries,' using a pronoun that refers back to something not yet mentioned. Paragraph 4 starts with 'Only 10% of the population,' which also needs prior context.

Concluding sentence: Why this is the last line? This paragraph is the last line because it summarizes the main points about Afghanistan's challenges. It uses Conclusive Words by providing final details about education and life expectancy, which wraps up the discussion.

Paragraph pairs:

• Pair 1 (Paragraph 1 → Paragraph 2): Paragraph 2 connects to Paragraph 1 because it continues the topic of Afghanistan. The Logical Order is clear as it moves from discussing a geographical feature to a route that goes through the country.
• Pair 2 (Paragraph 2 → Paragraph 3): Paragraph 3 links to Paragraph 2 because it gives more information about Afghanistan. The Broader to Specific Strategy is used here, as it moves from discussing a route to the economic condition of the country.
• Pair 3 (Paragraph 3 → Paragraph 4): Paragraph 4 connects to Paragraph 3 because it provides specific details about the poor conditions in Afghanistan. This follows the General to Specific Strategy, as it elaborates on the statement about poverty.