A.I. Explanation:

First sentence: Why this is the first line? This paragraph is the first sentence because it introduces the main topic of the text. It clearly states that genetic modification of crops is a topic of debate. This follows the rule of Topic Sentence. It does not refer to any previous information, so it stands alone. Why other lines are not chosen? The other paragraphs are not chosen because they do not meet the criteria for being independent. For example, Paragraph 2 starts with 'On the one hand,' which is a conjunction. Paragraph 3 starts with 'This,' which is a pronoun that refers back to something else. Paragraph 4 also starts with 'On the other hand,' which is a conjunction.

Concluding sentence: Why this is the last line? This paragraph is the last sentence because it wraps up the discussion by presenting the concerns about GM crops. It does not introduce new ideas but summarizes the debate. This follows the Conclusive Words rule.

Paragraph pairs:

• Pair 1 (Paragraph 1 → Paragraph 2): Paragraph 2 connects with Paragraph 1 because it uses the connector 'On the one hand.' This shows that it is giving one side of the debate mentioned in Paragraph 1. This follows the Connector Strategy.
• Pair 2 (Paragraph 2 → Paragraph 3): Paragraph 3 connects with Paragraph 2 because it explains the benefits of genetically modified crops. It shows how these crops can help with food security. This follows the Broader to Specific Strategy.
• Pair 3 (Paragraph 3 → Paragraph 4): Paragraph 4 connects with Paragraph 3 because it presents the other side of the debate. It uses 'On the other hand' to show contrast. This follows the Contrast Strategy.