A.I. Explanation:

First sentence: Why this is the first line? This paragraph is the first sentence because it introduces the main topic. It tells us about the Lost City of Atlantis and who first mentioned it. This is a general statement that does not need other sentences for context. It does not start with a conjunction or use pronouns. Why other lines are not chosen? Paragraph 2 starts with 'He' which is a pronoun, so it cannot be independent. Paragraph 3 starts with 'Despite' which is a conjunction, so it cannot be independent. Paragraph 4 starts with 'Some' which is also a pronoun, so it cannot be independent.

Concluding sentence: Why this is the last line? This paragraph is the last sentence because it summarizes the different beliefs about Atlantis. It wraps up the discussion by showing that there are two main views, which reflects the overall theme of the text.

Paragraph pairs:

• Pair 1 (Paragraph 1 → Paragraph 2): Paragraph 2 connects with Paragraph 1 because it gives more details about Atlantis. The word 'He' refers back to Plato, which shows a clear link between the two sentences.
• Pair 2 (Paragraph 2 → Paragraph 3): Paragraph 3 connects with Paragraph 2 because it talks about the search for Atlantis. The phrase 'Despite extensive research' shows that there is a problem with finding Atlantis, which follows logically from the description in Paragraph 2.
• Pair 3 (Paragraph 3 → Paragraph 4): Paragraph 4 connects with Paragraph 3 because it presents different views about Atlantis. The phrase 'Some believe' introduces opinions about the unknown location, which follows from the uncertainty mentioned in Paragraph 3.