A.I. Explanation:

First sentence: Why this is the first line? This paragraph is the first sentence because it introduces the main topic about animals in the soil. It does not need another sentence for context. It is a general statement that sets up the theme of the text. Why other lines are not chosen? The other paragraphs are not chosen because they do not stand alone. For example, 'One square metre of fertile soil contains over 1000 million animals' starts with a specific detail and needs the first sentence for context. 'Many of them are too tiny to see with the naked eye' uses 'them' which refers back to animals, so it cannot be first. 'Fungi and bacteria break down plant and animal remains' talks about a different topic and needs context from previous sentences.

Concluding sentence: Why this is the last line? This paragraph is the last sentence because it wraps up the discussion by explaining the role of fungi and bacteria in the soil. It provides a conclusion to the topic of soil and its living organisms.

Paragraph pairs:

• Pair 1 (Paragraph 1 → Paragraph 2): Paragraph 2 connects to Paragraph 1 because it gives more specific information about the animals mentioned in Paragraph 1. This follows the Broader to Specific Strategy.
• Pair 2 (Paragraph 2 → Paragraph 3): Paragraph 3 connects to Paragraph 2 because it explains more about the animals in the soil. It uses the Noun Pronoun Rule, as 'them' refers back to 'animals' from Paragraph 2.
• Pair 3 (Paragraph 3 → Paragraph 4): Paragraph 4 connects to Paragraph 3 because it shifts the topic from animals to fungi and bacteria. This shows a change in focus, which is a logical order.