A.I. Explanation:

First sentence: Why this is the first line? This paragraph is the first sentence because it introduces the main topic of roses. It is a general statement about roses being popular and their meaning. 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 'Their', which is a pronoun that refers back to roses. This makes it dependent on the first sentence. Paragraph 3 also starts with 'Moreover', which is a conjunction that shows it is adding information, not starting a new idea. Paragraph 4 starts with 'Yet', which is also a conjunction and does not introduce a new topic.

Concluding sentence: Why this is the last line? This paragraph is the last sentence because it wraps up the discussion about roses. It gives a final thought about the care needed for roses. This follows the Conclusive Words rule, as it ends the topic by showing the effort involved in growing roses.

Paragraph pairs:

• Pair 1 (Paragraph 1 → Paragraph 2): This pair connects because Paragraph 2 explains why roses are popular. It follows the Broader to Specific Strategy. The first sentence gives a general idea about roses, and the second sentence gives more details about their appeal.
• Pair 2 (Paragraph 2 → Paragraph 3): This pair connects because Paragraph 3 gives specific examples of the colors mentioned in Paragraph 2. This follows the General→Specific progression. The second paragraph talks about the appeal, and the third paragraph explains it further.
• Pair 3 (Paragraph 3 → Paragraph 4): This pair connects because Paragraph 4 introduces a new idea about the care needed for roses. It shows a contrast to the previous paragraph. This follows the Contrast rule, as it shifts from discussing the beauty of roses to the effort needed to keep them beautiful.