A.I. Explanation:

First sentence: Why this is the first line? This paragraph is the first line because it introduces the main topic of health. It gives a broad overview of how we are living in a good time for health. It does not use any words that need prior context. Why other lines are not chosen? Paragraph 2 starts with "The expectation of life" which is specific and needs context. Paragraph 3 starts with "Man versus the motor-car!" which is not about health. Paragraph 4 starts with "But though" which shows it is not independent. Paragraph 5 starts with "Man versus the motor-car!" which is also not about health.

Concluding sentence: Why this is the last line? This paragraph is the last line because it wraps up the discussion about dangers. It shows the ongoing problem of road safety. It gives a strong ending to the topic.

Paragraph pairs:

• Pair 1 (Paragraph 1 → Paragraph 2): The second paragraph connects to the first because it continues the topic of health. It shows how health has improved with modern drugs and surgery. This is a logical order of ideas.
• Pair 2 (Paragraph 2 → Paragraph 3): The third paragraph follows the second because it talks about the result of better health care. When illnesses are cured, people can live longer. This shows a clear cause and effect relationship.
• Pair 3 (Paragraph 3 → Paragraph 4): The fourth paragraph connects to the third because it talks about living longer but also warns about dangers. It shows a contrast between living longer and the dangers on the roads.
• Pair 4 (Paragraph 4 → Paragraph 5): The fifth paragraph connects to the fourth because it continues the idea of danger. It talks about the battle between people and cars, which is related to the dangers mentioned in the fourth paragraph.