A.I. Explanation:

First sentence: Why this is the first line? This paragraph is the first sentence because it introduces the main topic of farming and protection of harvest. It does not need another sentence for context. It is a general statement about farming. Why other lines are not chosen? Paragraph 2 starts with 'About 4,500 years ago,' which needs context. Paragraph 3 starts with 'Today,' which is not general. Paragraph 4 starts with 'Every dollar invested,' which is specific and needs context.

Concluding sentence: Why this is the last line? This paragraph is the last sentence because it wraps up the discussion about pesticides by showing their economic benefits. It summarizes the main points made in the previous paragraphs.

Paragraph pairs:

• Pair 1 (Paragraph 1 → Paragraph 2): Paragraph 2 connects to Paragraph 1 because it gives a specific example of how humans have protected their harvest in the past. This follows the Broader to Specific Strategy.
• Pair 2 (Paragraph 2 → Paragraph 3): Paragraph 3 connects to Paragraph 2 because it shows how pesticide use has changed over time. This follows the Chronological Order rule.
• Pair 3 (Paragraph 3 → Paragraph 4): Paragraph 4 connects to Paragraph 3 because it explains the benefits of using pesticides today. This follows the Cause and Effect Relationship rule.