A.I. Explanation:

First sentence: Why this is the first line? This paragraph is the first because it introduces the main topic of central banks. It gives a broad overview of their role in the economy without going into details. This follows the rule of Topic Sentence. Why other lines are not chosen? Paragraph 2 starts with 'Their' which is a pronoun, so it cannot stand alone. Paragraph 3 starts with 'For example,' which is a connector, so it is not independent. Paragraph 4 also starts with 'Additionally,' which is a transitional phrase, making it not independent.

Concluding sentence: Why this is the last line? This paragraph is the last because it wraps up the discussion about central banks. It gives a final point about their role during crises, which reflects the overarching theme.

Paragraph pairs:

• Pair 1 (Paragraph 1 → Paragraph 2): Paragraph 2 connects with Paragraph 1 because it continues the idea of central banks. It explains their main goal, which is a logical order of information.
• Pair 2 (Paragraph 2 → Paragraph 3): Paragraph 3 connects with Paragraph 2 because it gives an example of how central banks achieve their goal. This follows the Broader to Specific Strategy.
• Pair 3 (Paragraph 3 → Paragraph 4): Paragraph 4 connects with Paragraph 3 because it adds more information about the role of central banks. It shows another function they have, which is a logical order.