A.I. Explanation:

First sentence: Why this is the first line? This paragraph is the first sentence because it introduces the main idea of the text. It tells us about Doctor Byron's belief in a link between diet and acne. This is a general statement that sets the stage for the rest of the text. It does not refer to any previous information, so it is independent. Why other lines are not chosen? Paragraph 2 starts with 'He' which is a pronoun. This means it refers back to someone mentioned before, so it is not independent. Paragraph 3 starts with 'Professor Fitzgerald' but it does not introduce a new idea. It assumes we know about the study already. Paragraph 4 starts with 'The women' which also refers back to a group mentioned later. Paragraph 5 starts with 'No link' which is a conclusion and does not introduce the topic.

Concluding sentence: Why this is the last line? This paragraph is the last sentence because it summarizes the findings of the study. It gives a clear conclusion about the research done on diet and acne. It wraps up the main idea of the text.

Paragraph pairs:

• Pair 1 (Paragraph 1 → Paragraph 2): Paragraph 2 connects to Paragraph 1 because it shows the action taken after Doctor Byron's belief. The word 'He' refers to Doctor Byron, showing a logical flow from belief to action.
• Pair 2 (Paragraph 2 → Paragraph 3): Paragraph 3 follows Paragraph 2 because it explains what happened after the study was set up. It shows the result of the convincing action.
• Pair 3 (Paragraph 3 → Paragraph 4): Paragraph 4 connects to Paragraph 3 because it describes what the study involved. It shows the next step in the research process.
• Pair 4 (Paragraph 4 → Paragraph 5): Paragraph 5 follows Paragraph 4 because it gives the outcome of the study. It shows what the researchers found after collecting the information.