A.I. Explanation:

First sentence: Why this is the first line? This paragraph is the first sentence because it introduces the main topic. It gives a clear statement about what the study found. This follows the rule of Topic Sentence. Why other lines are not chosen? The other paragraphs are not chosen because they do not stand alone. For example, Paragraph 2 starts with 'To test this theory,' which needs more context. Paragraph 3 starts with 'As in the previous study,' which also needs prior information. Paragraph 4 starts with 'In the thought of,' which does not introduce a new idea.

Concluding sentence: Why this is the last line? This paragraph is the last sentence because it wraps up the discussion about sound frequency. It gives a final thought on the topic, which follows the Conclusive Words rule.

Paragraph pairs:

• Pair 1 (Paragraph 1 → Paragraph 2): Paragraph 2 connects to Paragraph 1 because it explains how the study will be tested. This follows the Logical Order rule.
• Pair 2 (Paragraph 2 → Paragraph 3): Paragraph 3 connects to Paragraph 2 because it gives more details about the study. This follows the Broader to Specific Strategy.
• Pair 3 (Paragraph 3 → Paragraph 4): Paragraph 4 connects to Paragraph 3 because it discusses the idea of sound frequency. This follows the Same Theme rule.