A.I. Explanation:

First sentence: Why this is the first line? This paragraph is the first line because it introduces the topic of fossil fuels. It gives a broad overview of the problem with fossil fuels. It does not use any words that need prior context. Why other lines are not chosen? Paragraph 2 starts with "Renewable energy sources" which is specific and assumes knowledge of fossil fuels. Paragraph 3 starts with "This transition" which refers back to previous ideas. Paragraph 4 uses "the" in "the development" which assumes prior knowledge.

Concluding sentence: Why this is the last line? This paragraph is the last line because it wraps up the discussion. It summarizes the need for cleaner energy and connects back to the problem of fossil fuels.

Paragraph pairs:

• Pair 1 (Paragraph 1 → Paragraph 2): This pair connects because Paragraph 2 talks about renewable energy after discussing fossil fuels. It shows a logical order from the problem of fossil fuels to the solution of renewable energy.
• Pair 2 (Paragraph 2 → Paragraph 3): This pair connects because Paragraph 3 explains what countries are doing about renewable energy. It follows the idea of popularity with action taken by countries.
• Pair 3 (Paragraph 3 → Paragraph 4): This pair connects because Paragraph 4 talks about the importance of the transition mentioned in Paragraph 3. It shows a logical order from investment to the need for cleaner energy.