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 research. It clearly states what the researchers are studying. This follows the rule of Topic Sentence. Why other lines are not chosen? The other paragraphs do not qualify as the first sentence. For example, Paragraph 2 starts with 'Initially,' which is a transitional word. This means it cannot stand alone. Paragraph 3 uses 'Participants,' which refers back to the researchers. Paragraph 4 starts with 'Over time,' which also shows a sequence and cannot be independent.

Concluding sentence: Why this is the last line? This paragraph is the last sentence because it wraps up the findings of the research. It gives the final results and shows the conclusion of the study. This follows the Conclusive Words rule.

Paragraph pairs:

• Pair 1 (Paragraph 1 → Paragraph 2): Paragraph 2 connects with Paragraph 1 because it continues the idea of the research. It explains what the researchers did next. This follows the Logical Order rule.
• Pair 2 (Paragraph 2 → Paragraph 3): Paragraph 3 connects with Paragraph 2 because it gives more details about the groups. It shows what happened at the start of the study. This follows the Broader to Specific Strategy.
• Pair 3 (Paragraph 3 → Paragraph 4): Paragraph 4 connects with Paragraph 3 because it shows the results after some time. It explains what happened next. This follows the Cause and Effect Relationship rule.