A.I. Explanation:

First sentence: Why this is the first line? This paragraph is the first line because it introduces the main topic of the text. It tells us about Afghanistan and its geography. This follows the rule of Topic Sentence. It sets up the main idea without going into details. 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 north', which needs context. Paragraph 3 starts with 'One of the highest', which also needs more information. Paragraph 4 starts with 'The southern edge', which assumes we know what is being talked about. Paragraph 5 starts with 'Here', which needs a place to refer to.

Concluding sentence: Why this is the last line? This paragraph is the last line because it wraps up the information about the southern edge of the Hindu Kush. It gives a final detail about the climate there. This follows the rule of Conclusive Words, as it summarizes the conditions in that area.

Paragraph pairs:

• Pair 1 (Paragraph 1 → Paragraph 2): Paragraph 2 connects with Paragraph 1 because it gives more detail about the mountains in Afghanistan. This follows the Broader to Specific Strategy. The first sentence talks about Afghanistan, and the second talks about the Hindu Kush, which is a specific part of Afghanistan.
• Pair 2 (Paragraph 2 → Paragraph 3): Paragraph 3 connects with Paragraph 2 because it describes the area around the Hindu Kush. This follows the Logical Order rule. The second paragraph talks about the mountains, and the third talks about the plain that is north of these mountains.
• Pair 3 (Paragraph 3 → Paragraph 4): Paragraph 4 connects with Paragraph 3 because it describes another area of the Hindu Kush. This follows the Logical Order rule. The third paragraph talks about the plain, and the fourth talks about the southern edge, which is another part of the same mountain range.
• Pair 4 (Paragraph 4 → Paragraph 5): Paragraph 5 connects with Paragraph 4 because it gives more information about the southern edge of the Hindu Kush. This follows the Cause and Effect Relationship rule. The fourth paragraph talks about the desert, and the fifth explains what happens there, like high temperatures and dust storms.