A.I. Explanation:

First sentence: Why this is the first line? This paragraph is the first sentence because it gives a clear topic about drug resistance. It talks about the main issue of breast cancer deaths. This is an important introduction to the topic. It does not use any words that need other sentences for meaning. Why other lines are not chosen? Paragraph 2 starts with 'Now,' which is a conjunction. Paragraph 3 starts with 'The connection,' which needs more context. Paragraph 4 starts with 'The work,' which also needs prior information. All these sentences do not stand alone.

Concluding sentence: Why this is the last line? This paragraph is the last sentence because it wraps up the ideas about drug resistance and dietary changes. It shows a conclusion about what can be done next. It gives a final thought on the topic.

Paragraph pairs:

• Pair 1 (Paragraph 1 → Paragraph 2): Paragraph 2 connects to Paragraph 1 because it continues the topic of drug resistance. It uses the word 'Now' to show a new finding related to the same issue.
• Pair 2 (Paragraph 2 → Paragraph 3): Paragraph 3 connects to Paragraph 2 because it explains what the researchers found. It talks about leucine, which is the dietary element mentioned in Paragraph 2. This shows a logical order of ideas.
• Pair 3 (Paragraph 3 → Paragraph 4): Paragraph 4 connects to Paragraph 3 because it talks about the next step after the dietary change. It mentions the possibility of a drug, which relates to the dietary restriction discussed in Paragraph 3. This shows a clear flow of ideas.