First sentence: Why this is the first line? This paragraph is the first line because it introduces the main topic of earthquakes. It does not refer to any previous information. It gives a broad overview of the subject. This follows the rule of Topic Sentence. Why other lines are not chosen? Paragraph 2 starts with 'It was necessary,' which refers to something that needs context. Paragraph 3 starts with 'Some devices,' which also needs context. Paragraph 4 starts with 'One, for instance,' which is not independent. Paragraph 5 starts with 'When a shock came,' which suggests a specific event and needs prior information.

Concluding sentence: Why this is the last line? This paragraph is the last line because it describes the result of the previous information. It wraps up the discussion about the instruments and their function. This follows the Summary Style rule.

Paragraph pairs:

• Pair 1 (Paragraph 1 → Paragraph 2): Paragraph 2 connects to Paragraph 1 because it explains the need for instruments after mentioning earthquakes. This follows the Logical Order rule.
• Pair 2 (Paragraph 2 → Paragraph 3): Paragraph 3 connects to Paragraph 2 because it gives examples of the instruments mentioned. This follows the Broader to Specific Strategy.
• Pair 3 (Paragraph 3 → Paragraph 4): Paragraph 4 connects to Paragraph 3 because it provides a specific example of the simple devices. This follows the Topic Example rule.
• Pair 4 (Paragraph 4 → Paragraph 5): Paragraph 5 connects to Paragraph 4 because it describes what happens when the devices are used. This follows the Cause and Effect Relationship rule.