A.I. Explanation:

First sentence: Why this is the first line? This paragraph is the first sentence because it introduces the main topic. It gives a broad overview of what the text is about. It does not need any other sentence for context. It does not use any pronouns or definite articles that refer to previous ideas. Why other lines are not chosen? Paragraph 2 starts with 'Built' which is a past participle and does not stand alone. Paragraph 3 starts with 'The construction methods' which uses 'the' and assumes prior knowledge. Paragraph 4 starts with 'Furthermore' which is a conjunction and shows continuation, so it cannot be first.

Concluding sentence: Why this is the last line? This paragraph is the last sentence because it wraps up the discussion. It summarizes the unknown aspects of the Great Zimbabwe. It uses the word 'remain' which shows that the topic is still open and unresolved.

Paragraph pairs:

• Pair 1 (Paragraph 1 → Paragraph 2): Paragraph 2 connects with Paragraph 1 because it gives more specific information about the Great Zimbabwe. This follows the Broader to Specific Strategy. The first sentence introduces the city, and the second sentence explains its historical importance.
• Pair 2 (Paragraph 2 → Paragraph 3): Paragraph 3 connects with Paragraph 2 because it continues to discuss the Great Zimbabwe. It shows the Logical Order of ideas. After talking about its history, it mentions what is not known about the city.
• Pair 3 (Paragraph 3 → Paragraph 4): Paragraph 4 connects with Paragraph 3 because it continues the discussion about what is unknown. It uses the Connector 'Furthermore' to show that it adds more information about the mysteries of the Great Zimbabwe.