First sentence: Why this is the first line? This paragraph is the first sentence because it introduces the main topic of human existence. It does not need any other sentence for context. It is a general statement that sets up the theme of the text. Why other lines are not chosen? Paragraph 2 starts with "Ancient Greek philosophers" which refers to specific people and needs context. Paragraph 3 starts with "With the discovery" which also needs prior information. Paragraph 4 starts with "While there may be no single conclusion" which suggests a discussion that needs earlier sentences for understanding.

Concluding sentence: Why this is the last line? This paragraph is the last sentence because it wraps up the discussion. It gives a final thought about human uniqueness after discussing theories. It summarizes the main idea of the text.

Paragraph pairs:

• Pair 1 (Paragraph 1 → Paragraph 2): Paragraph 2 connects to Paragraph 1 because it continues the discussion about human existence. It uses the topic introduced in Paragraph 1 and gives examples of philosophers who thought about this topic. This shows a logical order from a general idea to specific examples.
• Pair 2 (Paragraph 2 → Paragraph 3): Paragraph 3 connects to Paragraph 2 because it continues the theme of theories about human existence. It shows that not only philosophers have theories, but scientists do too. This is a logical order from philosophers to scientists.
• Pair 3 (Paragraph 3 → Paragraph 4): Paragraph 4 connects to Paragraph 3 because it discusses the outcome of all the theories. It shows that even with many theories, there is a strong belief about human uniqueness. This is a logical order from scientific theories to a conclusion about humans.