A.I. Explanation:

First sentence: Why this is the first line? This paragraph is the first sentence because it introduces the main topic of the text, which is the Sun's energy. It does not need another sentence for context. It does not start with a conjunction or use a pronoun. It also does not use the definite article 'the' for a defined subject. Why other lines are not chosen? Paragraph 2 starts with 'Turning', which is a gerund and does not stand alone. Paragraph 3 uses 'On a sunny day', which is a specific situation and not general. Paragraph 4 starts with 'In fact', which is a conjunction. Paragraph 5 starts with 'The equipment', which uses the definite article and assumes prior knowledge.

Concluding sentence: Why this is the last line? This paragraph is the last sentence because it wraps up the discussion about solar power. It gives a conclusion about the costs of using solar energy compared to ordinary power-stations. It summarizes the main points made in the text.

Paragraph pairs:

• Pair 1 (Paragraph 1 → Paragraph 2): This pair connects because the second sentence explains what we can do with the light and heat from the Sun. It uses the 'Broader to Specific Strategy' where the first sentence gives a general idea about the Sun's energy and the second sentence specifies how we can use that energy.
• Pair 2 (Paragraph 2 → Paragraph 3): This pair connects because the third sentence gives an example of solar power in action. It uses the 'Topic Example' strategy where the second sentence introduces solar power and the third sentence provides a specific example of how much power can be collected.
• Pair 3 (Paragraph 3 → Paragraph 4): This pair connects because the fourth sentence discusses the potential of solar power. It uses the 'Logical Order' strategy where the third sentence gives a specific example of solar power, and the fourth sentence explains the larger potential of that power.
• Pair 4 (Paragraph 4 → Paragraph 5): This pair connects because the fifth sentence discusses the practical side of using solar power. It uses the 'Cause and Effect Relationship' strategy where the fourth sentence talks about the potential of solar power, and the fifth sentence explains the costs involved in using that power.