A.I. Explanation:

First sentence: Why this is the first line? This paragraph is the first line because it introduces the main topic of the text. It talks about the government's promise to reduce carbon emissions. This is a broad overview of the subject. It does not use any pronouns or definite articles that refer to previous information. Why other lines are not chosen? Paragraph 2 starts with "And" which is a conjunction, so it cannot be the first sentence. Paragraph 3 starts with "But" which is also a conjunction. Paragraph 4 uses the definite article "the" which assumes prior knowledge, so it cannot be independent.

Concluding sentence: Why this is the last line? This paragraph is the last line because it wraps up the discussion. It provides a specific example of the consequences of using tidal energy. It summarizes the earlier points about the challenges and concerns.

Paragraph pairs:

• Pair 1 (Paragraph 1 → Paragraph 2): Paragraph 2 connects with Paragraph 1 because it continues the idea of reducing carbon emissions. The phrase "And with the second largest tidal range" shows a logical order. It explains how British marine energy can help in this effort.
• Pair 2 (Paragraph 2 → Paragraph 3): Paragraph 3 connects with Paragraph 2 because it introduces a contrast. The word "But" shows that there are challenges in using tidal energy. This is a cause and effect relationship.
• Pair 3 (Paragraph 3 → Paragraph 4): Paragraph 4 connects with Paragraph 3 because it gives an example of the consequences mentioned. It shows a logical order by providing evidence of the challenges in using tidal energy.