First sentence: Why this is the first line? This paragraph is the first sentence because it introduces the main topic of underground water. It gives a broad overview of how underground water works without going into details. It does not use any pronouns or definite articles that need prior context. Why other lines are not chosen? The other paragraphs are not independent. For example, Paragraph 2 starts with 'But', which is a conjunction. Paragraph 3 uses 'These', which refers back to something not yet mentioned. Paragraph 4 starts with 'But', which is also a conjunction. Paragraph 5 uses 'This', which refers back to something not yet introduced.

Concluding sentence: Why this is the last line? This paragraph is the last sentence because it wraps up the discussion. It shows the result of the previous problems and gives a clear conclusion about the need for pumping water.

Paragraph pairs:

• Pair 1 (Paragraph 1 → Paragraph 2): Paragraph 2 connects to Paragraph 1 because it continues the idea of underground water. It uses the phrase 'from these underground reservoirs' to show where the water comes from, making a logical flow of ideas.
• Pair 2 (Paragraph 2 → Paragraph 3): Paragraph 3 connects to Paragraph 2 because it explains the importance of the springs mentioned in Paragraph 2. It gives specific examples of who used the water, showing a broader to specific strategy.
• Pair 3 (Paragraph 3 → Paragraph 4): Paragraph 4 connects to Paragraph 3 because it introduces a contrast. It shows that while the springs were important, there is a problem now with water levels falling, using the connector 'But'.
• Pair 4 (Paragraph 4 → Paragraph 5): Paragraph 5 connects to Paragraph 4 because it explains the result of the problem mentioned in Paragraph 4. It shows that because of low water levels, pumping is needed, which follows a cause and effect relationship.