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 chess. It gives a broad overview of chess as an old and scientific game. 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 as the first sentence. For example, 'It was first mentioned...' starts with 'It', which is a pronoun. 'The origins of this game...' is a general statement but does not introduce the topic. 'It was originally played...' also starts with 'It', and 'It is said that...' starts with 'It', which is not independent.

Concluding sentence: Why this is the last line? This paragraph is the last sentence because it wraps up the discussion about chess. It gives a final thought on its purpose, which is to teach the art of war. This follows the rule of Conclusive Words, as it summarizes the main idea.

Paragraph pairs:

• Pair 1 (Paragraph 1 → Paragraph 2): Paragraph 2 connects with Paragraph 1 because it continues the topic of chess. It uses the Logical Order rule, as it moves from a general statement about chess to a specific point about its origins.
• Pair 2 (Paragraph 2 → Paragraph 3): Paragraph 3 connects with Paragraph 2 because it gives more detail about the origins of chess. This follows the Broader to Specific Strategy, as it goes from a general idea about origins to a specific historical fact.
• Pair 3 (Paragraph 3 → Paragraph 4): Paragraph 4 connects with Paragraph 3 because it provides more information about who played chess. This uses the Logical Order rule, as it continues the narrative about chess's history.
• Pair 4 (Paragraph 4 → Paragraph 5): Paragraph 5 connects with Paragraph 4 because it explains why chess was played by kings. This follows the Cause and Effect Relationship rule, as it shows the reason behind the game's invention.