A.I. Explanation:

First sentence: Why this is the first line? This paragraph is the first sentence because it introduces the main topic. It is a general statement about a scientist. It does not need other sentences to understand it. It does not use any pronouns or definite articles that refer to previous ideas. Why other lines are not chosen? The other paragraphs are not chosen because they do not meet the criteria for being independent. For example, 'He lost his memory...' starts with a pronoun 'He', so it is not independent. 'But when he is hungry...' starts with a conjunction 'But', so it is not independent. 'The scientists have studied...' uses the definite article 'the', which means it refers to something already known, so it is not independent.

Concluding sentence: Why this is the last line? This paragraph is the last sentence because it wraps up the topic. It gives a conclusion about memory and what scientists have found. It summarizes the main idea of the text.

Paragraph pairs:

• Pair 1 (Paragraph 1 → Paragraph 2): This pair connects because the second sentence gives more information about the scientist. It shows a problem related to the scientist's health.
• Pair 2 (Paragraph 2 → Paragraph 3): This pair connects because the third sentence explains what happens when the scientist is hungry. It shows a cause and effect relationship.
• Pair 3 (Paragraph 3 → Paragraph 4): This pair connects because the fourth sentence gives a broader explanation about memory. It shows that scientists have studied how the brain works.