A.I. Explanation:

First sentence: Why this is the first line? This paragraph is the first sentence because it introduces the main topic of language learning. It gives a broad overview of how most people think about learning a language. It does not use any pronouns or definite articles that need prior context. Why other lines are not chosen? Paragraph 2 starts with "Unfortunately," which is a conjunction. Paragraph 3 starts with "What's more," which is also a conjunction. Paragraph 4 starts with "So," which is a conjunction too. All these sentences cannot stand alone without needing another sentence for context.

Concluding sentence: Why this is the last line? This paragraph is the last sentence because it wraps up the discussion about language learning. It uses the phrase "So it's clear that" which signals a conclusion. It reflects on the main ideas presented in the earlier paragraphs.

Paragraph pairs:

• Pair 1 (Paragraph 1 → Paragraph 2): Paragraph 2 connects with Paragraph 1 because it shows the problem with the linear approach. The word "Unfortunately" is a connector that shows a negative result of the idea in Paragraph 1.
• Pair 2 (Paragraph 2 → Paragraph 3): Paragraph 3 connects with Paragraph 2 because it gives more details about the long journey of language learning. The phrase "What's more" shows that it adds more information to the idea in Paragraph 2.
• Pair 3 (Paragraph 3 → Paragraph 4): Paragraph 4 connects with Paragraph 3 because it explains the need for the right mental approach. The word "So" shows that it is a conclusion based on the ideas in Paragraph 3.