First sentence: Why this is the first line? This paragraph is the first sentence because it introduces the main topic of particles and their behavior. It does not need another sentence for context. It gives a broad overview of the topic. Why other lines are not chosen? Paragraph 2 starts with 'A new device' which is not independent. Paragraph 3 starts with 'Slight changes' which also needs context. Paragraph 4 starts with 'This allows' which refers back to something else. Paragraph 5 starts with 'In a first test-run' which needs prior information.

Concluding sentence: Why this is the last line? This paragraph is the last sentence because it provides a specific example of the device in action. It wraps up the discussion by showing a real-world application of the technology.

Paragraph pairs:

• Pair 1 (Paragraph 1 → Paragraph 2): This pair connects because the second paragraph explains how the strange behavior of particles is used in a new device. It follows a logical order from the general idea of particles to a specific application.
• Pair 2 (Paragraph 2 → Paragraph 3): This pair connects because the third paragraph explains what happens when the device measures gravity. It shows a cause and effect relationship where the device's function leads to understanding changes in density.
• Pair 3 (Paragraph 3 → Paragraph 4): This pair connects because the fourth paragraph explains the result of the changes in gravity. It shows how the information from the sensor helps detect underground objects.
• Pair 4 (Paragraph 4 → Paragraph 5): This pair connects because the fifth paragraph gives an example of the instrument's detection ability. It follows a logical order from the general function to a specific instance.