A.I. Explanation:

First sentence: Why this is the first line? This paragraph is the first sentence because it introduces the main topic of livestock in agriculture. It is a general statement that does not need another sentence for context. It does not start with a conjunction or use pronouns. Why other lines are not chosen? Paragraph 2 starts with 'They', which is a pronoun and needs context. Paragraph 3 starts with 'However', which is a conjunction. Paragraph 4 starts with 'Thus', which is also a conjunction.

Concluding sentence: Why this is the last line? This paragraph is the last sentence because it wraps up the discussion. It shows the result of the previous points about livestock farming and the need for sustainability. The word 'Thus' signals that it is concluding the topic.

Paragraph pairs:

• Pair 1 (Paragraph 1 → Paragraph 2): Paragraph 2 connects to Paragraph 1 because it gives more details about livestock. This follows the Broader to Specific Strategy, where the first sentence is general and the second gives specific information.
• Pair 2 (Paragraph 2 → Paragraph 3): Paragraph 3 connects to Paragraph 2 because it introduces a contrast. The word 'However' shows that there is a problem with intensive livestock farming. This follows the Contrast rule.
• Pair 3 (Paragraph 3 → Paragraph 4): Paragraph 4 connects to Paragraph 3 because it shows a solution to the problems mentioned. The word 'Thus' indicates that there is a result from the concerns raised. This follows the Cause and Effect Relationship rule.