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 rank of a captain in the US Army. It does not need another sentence for context. It is a general statement about the rank. Why other lines are not chosen? Paragraph 2 starts with 'They', which is a pronoun and needs context. Paragraph 3 also starts with 'The', which refers to a specific subject that is not introduced yet. Paragraph 4 starts with 'The majors', which also assumes prior knowledge. All these do not stand alone.

Concluding sentence: Why this is the last line? This paragraph is the last sentence because it wraps up the discussion about ranks in the army. It gives a summary of the roles of majors, which is the final point in the text.

Paragraph pairs:

• Pair 1 (Paragraph 1 → Paragraph 2): Paragraph 2 connects with Paragraph 1 because it continues the topic of ranks in the army. The phrase 'They rank above' shows a logical order of ranks.
• Pair 2 (Paragraph 2 → Paragraph 3): Paragraph 3 connects with Paragraph 2 because it explains more about the first lieutenant. It shows a logical order from ranks to responsibilities.
• Pair 3 (Paragraph 3 → Paragraph 4): Paragraph 4 connects with Paragraph 3 because it shifts to the majors. It shows a broader topic about army ranks and their roles.