A.I. Explanation:

First sentence: Why this is the first line? This paragraph is the first sentence because it introduces the main topic about mosquitoes. It is a general statement that does not need other sentences for context. It does not start with a conjunction or a pronoun. It sets the scene for the discussion about mosquitoes. Why other lines are not chosen? Paragraph 2 starts with "These insects" which refers back to mosquitoes, so it is not independent. Paragraph 3 starts with "They" which is a pronoun referring to mosquitoes, so it is not independent. Paragraph 4 starts with "But" which is a conjunction, so it is not independent.

Concluding sentence: Why this is the last line? This paragraph is the last sentence because it wraps up the discussion. It shows that there was a lack of knowledge about mosquitoes before. The phrase "But until now" signals a conclusion to the earlier points.

Paragraph pairs:

• Pair 1 (Paragraph 1 → Paragraph 2): Paragraph 2 connects with Paragraph 1 because it continues the topic of mosquitoes. The phrase "These insects" refers back to mosquitoes, showing a clear link. This is an example of the Noun Pronoun Rule.
• Pair 2 (Paragraph 2 → Paragraph 3): Paragraph 3 connects with Paragraph 2 because it adds more information about mosquitoes. The word "They" refers back to "These insects," showing a clear link. This is an example of the Noun Pronoun Rule.
• Pair 3 (Paragraph 3 → Paragraph 4): Paragraph 4 connects with Paragraph 3 because it introduces new information about mosquitoes. The word "But" shows a contrast to what was said before, linking the ideas. This is an example of the Connector Strategy.