A.I. Explanation:

First sentence: Why this is the first line? This paragraph is the first sentence because it introduces the main topic, which is the theory of relativity. It does not refer to any previous information. It gives a broad overview of what the paragraph is about. 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 'It', which is a pronoun that refers back to the theory. This makes it dependent on the first sentence. Paragraph 3 also starts with 'It', and Paragraph 4 starts with 'Furthermore', which is a connector. These words show that they need more context to make sense.

Concluding sentence: Why this is the last line? This paragraph is the last sentence because it summarizes the impact of the theory of relativity. It wraps up the discussion by showing how the theory has changed our understanding. This follows the rule of Conclusive Words.

Paragraph pairs:

• Pair 1 (Paragraph 1 → Paragraph 2): Paragraph 2 connects with Paragraph 1 because it continues the idea of the theory of relativity. The phrase 'It posits' refers back to 'the theory of relativity'. This follows the Noun Pronoun Rule.
• Pair 2 (Paragraph 2 → Paragraph 3): Paragraph 3 connects with Paragraph 2 because it adds more information about the theory. The word 'Furthermore' shows that it is giving more details. This follows the Connector Strategy.
• Pair 3 (Paragraph 3 → Paragraph 4): Paragraph 4 connects with Paragraph 3 because it shows the effect of the theory. The phrase 'As a result' indicates that the information in Paragraph 4 is a consequence of what was said in Paragraph 3. This follows the Cause and Effect Relationship.