First sentence: Why this is the first line? This paragraph is the first sentence because it introduces the main topic of green architecture. It does not use any pronouns or definite articles that refer to previous ideas. It clearly states the main idea without needing other sentences for context. Why other lines are not chosen? The other paragraphs are not chosen because they do not stand alone. For example, Paragraph 2 starts with 'It', which is a pronoun and needs context. Paragraph 3 also starts with 'These', which refers back to something not yet mentioned. Paragraph 4 starts with 'However', which is a conjunction and shows a contrast, so it cannot be the first sentence.

Concluding sentence: Why this is the last line? This paragraph is the last sentence because it presents a challenge or a downside to green architecture. It does not introduce new ideas but wraps up the discussion by showing a different perspective. This follows the Conclusive Words rule, as it gives a final thought on the topic.

Paragraph pairs:

• Pair 1 (Paragraph 1 → Paragraph 2): Paragraph 2 connects with Paragraph 1 because it gives more details about green architecture. This follows the Broader to Specific Strategy. The first sentence talks about the main idea, and the second sentence explains how this idea is put into practice.
• Pair 2 (Paragraph 2 → Paragraph 3): Paragraph 3 connects with Paragraph 2 because it explains the benefits of the systems mentioned. This follows the Logical Order rule. The second sentence talks about what is included in green architecture, and the third sentence explains the positive effects of those practices.
• Pair 3 (Paragraph 3 → Paragraph 4): Paragraph 4 connects with Paragraph 3 because it introduces a contrasting idea. This follows the Contrast rule. The third sentence talks about the benefits of green practices, while the fourth sentence mentions a challenge related to the initial costs.