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 talks about September in Delhi and gives a broad overview of the season. It does not refer to any previous information. 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 'But', which is a conjunction. Paragraph 3 starts with 'As a result', which also shows it is not independent. Paragraph 4 uses 'Nevertheless', which is another conjunction. These words show that they need more context to make sense.

Concluding sentence: Why this is the last line? This paragraph is the last line because it wraps up the situation described in the text. It shows the final feeling of discomfort after unpacking. The phrase 'in conclusion' is not used, but it summarizes the experience well.

Paragraph pairs:

• Pair 1 (Paragraph 1 → Paragraph 2): Paragraph 2 connects with Paragraph 1 because it gives a specific situation about the year of arrival. The word 'But' shows a contrast to the good conditions mentioned in Paragraph 1. This follows the Contrast rule.
• Pair 2 (Paragraph 2 → Paragraph 3): Paragraph 3 connects with Paragraph 2 because it explains the effect of the short monsoon rains. The phrase 'As a result' shows that the dust everywhere is a consequence of the previous information. This follows the Cause and Effect Relationship rule.
• Pair 3 (Paragraph 3 → Paragraph 4): Paragraph 4 connects with Paragraph 3 because it describes the conditions after the dust. The word 'Nevertheless' shows that even with the dust, the air was still uncomfortable. This follows the Contrast rule.