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 gives a broad overview of what the study is about without going into details. It does not use any pronouns or definite articles that refer to previous information. Why other lines are not chosen? Paragraph 2 starts with "Sometimes" which is a conjunction, so it cannot be independent. Paragraph 3 uses "There were" which does not stand alone as an introduction. Paragraph 4 uses "This study" which assumes prior knowledge, making it not independent.

Concluding sentence: Why this is the last line? This paragraph is the last sentence because it summarizes the findings of the study. It wraps up the main points and shows the results of the research.

Paragraph pairs:

• Pair 1 (Paragraph 1 → Paragraph 2): This pair connects because Paragraph 2 gives an example of how the babies were dressed, which relates to the research in Paragraph 1. This shows a logical order from the general research to a specific example.
• Pair 2 (Paragraph 2 → Paragraph 3): This pair connects because Paragraph 3 explains the toys that relate to the dressing of the infants in Paragraph 2. It shows a logical order from the description of the infants to the toys available.
• Pair 3 (Paragraph 3 → Paragraph 4): This pair connects because Paragraph 4 discusses the findings of the study based on the toys mentioned in Paragraph 3. It shows a logical order from the toys to the results of how babies were treated.