A.I. Explanation:

First sentence: Why this is the first line? This paragraph is the first sentence because it introduces the main idea of the savannah hypothesis. It gives a clear overview of the topic without needing other sentences for context. It does not use any pronouns or definite articles that refer to previous ideas. Why other lines are not chosen? Paragraph 2 starts with "One," which shows it is not independent. Paragraph 3 starts with "Scientists," which uses a pronoun. Paragraph 4 starts with "Hominids," which is too specific. Paragraph 5 starts with "Scientists," which also uses a pronoun.

Concluding sentence: Why this is the last line? This paragraph is the last sentence because it summarizes the discussion about the evolution of hominids. It wraps up the main ideas presented in the previous paragraphs.

Paragraph pairs:

• Pair 1 (Paragraph 1 → Paragraph 2): This pair connects because Paragraph 2 uses the word "One" to introduce a new idea after the first hypothesis. This shows a logical order of ideas.
• Pair 2 (Paragraph 2 → Paragraph 3): This pair connects because Paragraph 3 gives a specific example of what happened after the hypotheses. It shows a logical order from general ideas to specific events.
• Pair 3 (Paragraph 3 → Paragraph 4): This pair connects because Paragraph 4 explains how hominids evolved after migrating. It shows a logical order of events.
• Pair 4 (Paragraph 4 → Paragraph 5): This pair connects because Paragraph 5 discusses the theories about evolution after stating that hominids evolved. It shows a logical order of ideas.