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 text. It shows a shift in thinking about how food allergies happen. This follows the rule of Topic Sentence. It does not refer to any previous information, so it stands alone. Why other lines are not chosen? The other paragraphs are not chosen because they do not meet the criteria for being independent. For example, Paragraph 2 starts with "Several" which does not stand alone. Paragraph 3 starts with "First" which shows it is not independent. Paragraph 4 starts with "Then" which also shows it is not independent. Paragraph 5 starts with "Altogether" which indicates it is not independent.

Concluding sentence: Why this is the last line? This paragraph is the last sentence because it wraps up the main ideas of the text. It uses conclusive words like "Altogether" to show it is a summary. It reflects the overall theme of the importance of skin sensitization in food allergies.

Paragraph pairs:

• Pair 1 (Paragraph 1 → Paragraph 2): Paragraph 2 connects to Paragraph 1 because it continues the idea about the skin. It uses the Logical Order rule, showing how the topic of skin is important after discussing the shift in thinking.
• Pair 2 (Paragraph 2 → Paragraph 3): Paragraph 3 connects to Paragraph 2 because it gives a specific example of the observations about the skin. This follows the Broader to Specific Strategy, where the general idea about skin is followed by a specific observation.
• Pair 3 (Paragraph 3 → Paragraph 4): Paragraph 4 connects to Paragraph 3 because it continues the discussion about food allergy. It uses the Cause and Effect Relationship rule, showing how the observation leads to findings about skin barrier proteins.
• Pair 4 (Paragraph 4 → Paragraph 5): Paragraph 5 connects to Paragraph 4 because it summarizes the importance of skin sensitization. This follows the Topic Closure rule, bringing together the ideas about skin and food allergy.