A.I. Explanation:

First sentence: Why this is the first line? This paragraph is the first line because it introduces the main topic of soil and its small living things. It does not need another sentence for context. It gives a broad overview of what affects soil. Why other lines are not chosen? The other paragraphs are not chosen because: 1) "Surprisingly, earthworms..." starts with a transitional word, so it is not independent. 2) "Ants, beetles, centipedes..." starts with a conjunction, so it is not independent. 3) "Earthworms tunnel..." does not introduce the topic of soil and its small living things.

Concluding sentence: Why this is the last line? This paragraph is the last line because it wraps up the discussion about life in the soil. It gives a summary of different animals that live in the soil, which connects back to the main topic.

Paragraph pairs:

• Pair 1 (Paragraph 1 → Paragraph 2): Paragraph 2 connects with Paragraph 1 because it continues the topic of soil. The first paragraph talks about tiny living things in soil, and the second talks about earthworms, which are also important for soil.
• Pair 2 (Paragraph 2 → Paragraph 3): Paragraph 3 connects with Paragraph 2 because it gives more information about earthworms. It shows how much soil earthworms can move, which is a specific detail about their role in soil.
• Pair 3 (Paragraph 3 → Paragraph 4): Paragraph 4 connects with Paragraph 3 because it shifts the focus from earthworms to other animals in the soil. It shows a broader view of life in the soil after discussing earthworms.