First sentence: Why this is the first line? This paragraph is the first sentence because it introduces the main topic about the history of books. It does not need other sentences for context. It gives a broad overview of the topic. It does not use any pronouns or definite articles that refer to previous ideas. Why other lines are not chosen? Paragraph 2 starts with 'By the 4th century,' which needs a time context, so it is not independent. Paragraph 3 starts with 'Early in the Middle Ages,' which also needs context. Paragraph 4 starts with 'But the only way,' which refers back to previous ideas, so it is not independent.

Concluding sentence: Why this is the last line? This paragraph is the last sentence because it wraps up the discussion about making books. It gives a final thought on how books were made in the past.

Paragraph pairs:

• Pair 1 (Paragraph 1 → Paragraph 2): Paragraph 2 connects with Paragraph 1 because it continues the story of books. It shows a logical order from the early attempts at books to the development of books with pages.
• Pair 2 (Paragraph 2 → Paragraph 3): Paragraph 3 connects with Paragraph 2 because it explains how books were made. It shows a logical order from having books to learning how to make paper.
• Pair 3 (Paragraph 3 → Paragraph 4): Paragraph 4 connects with Paragraph 3 because it gives more details about paper. It shows a logical order from the introduction of paper to its advantages.
• Pair 4 (Paragraph 4 → Paragraph 5): Paragraph 5 connects with Paragraph 4 because it explains the process of making books. It shows a logical order from the benefits of paper to the method of creating books.