A.I. Explanation:

First sentence: Why this is the first line? This paragraph is the first line because it introduces the main topic. It tells us about the researchers and their goal. This is a clear overview of what the text will discuss. It does not use any words that need prior context. Why other lines are not chosen? Paragraph 2 starts with "Only" which is a conjunction, so it cannot be independent. Paragraph 3 starts with "The elephants" but it refers back to the elephants without introducing them first. Paragraph 4 starts with "The elephants" too, which also assumes prior knowledge. So, they cannot be the first sentence.

Concluding sentence: Why this is the last line? This paragraph is the last line because it wraps up the main idea. It explains the conclusion about the elephants' reaction to the drones. It gives a final thought on the topic.

Paragraph pairs:

• Pair 1 (Paragraph 1 → Paragraph 2): This pair connects because Paragraph 2 shows a problem that happened after the plan in Paragraph 1. It uses the word "Only" to show that something went wrong.
• Pair 2 (Paragraph 2 → Paragraph 3): This pair connects because Paragraph 3 explains what went wrong. The elephants reacted to the drones, which is the problem mentioned in Paragraph 2.
• Pair 3 (Paragraph 3 → Paragraph 4): This pair connects because Paragraph 4 explains why the elephants reacted strongly. It gives the reason for their behavior mentioned in Paragraph 3.