First sentence: Why this is the first line? This paragraph is the first sentence because it introduces the main topic of the text. It talks about meteorite impacts and their effects on life. This is a broad overview of the subject. It does not use any words that need prior context. Why other lines are not chosen? The other paragraphs are not chosen because they do not stand alone. For example, Paragraph 2 starts with "According to some estimates," which needs prior information. Paragraph 3 starts with "Yet," which is a conjunction. Paragraph 4 uses "the majority," which assumes prior knowledge. Paragraph 5 starts with "Yet an equally important criterion," which also needs context.

Concluding sentence: Why this is the last line? This paragraph is the last sentence because it wraps up the discussion about survival criteria. It introduces an important point that relates back to the impacts mentioned earlier. It does not need more information after it.

Paragraph pairs:

• Pair 1 (Paragraph 1 → Paragraph 2): Paragraph 2 connects to Paragraph 1 because it gives specific information about the impacts mentioned in Paragraph 1. It uses the connector "According to some estimates," which shows that it is related to the topic of impacts.
• Pair 2 (Paragraph 2 → Paragraph 3): Paragraph 3 connects to Paragraph 2 because it explains how the information in Paragraph 2 changes our understanding. The phrase "Such a perspective" refers back to the idea of extinctions from impacts.
• Pair 3 (Paragraph 3 → Paragraph 4): Paragraph 4 connects to Paragraph 3 because it introduces a standard criterion for survival. It shows a different aspect of evolution, moving from the perspective of impacts to the criteria for survival.
• Pair 4 (Paragraph 4 → Paragraph 5): Paragraph 5 connects to Paragraph 4 because it presents another important criterion for survival. The word "Yet" shows a contrast between the two criteria, linking them together.