A.I. Explanation:

First sentence: Why this is the first line? This paragraph is the first sentence because it introduces the main topic of the text. It tells us who invented the float process for making flat glass. This is a clear topic sentence that sets up the main idea without going into details. It does not use any pronouns or definite articles that would 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 'This process,' which refers back to the float process, so it cannot be first. Paragraph 3 starts with 'Pilkington,' which assumes we know who Pilkington is. Paragraph 4 uses 'The metal,' which also assumes prior knowledge. Paragraph 5 starts with 'The best metal,' which again assumes we know what metal is being talked about.

Concluding sentence: Why this is the last line? This paragraph is the last sentence because it concludes the discussion about the float process. It gives the final detail about the best metal to use, which wraps up the topic.

Paragraph pairs:

• Pair 1 (Paragraph 1 → Paragraph 2): Paragraph 2 connects with Paragraph 1 because it uses the connector 'This process.' This shows that it is talking about the float process mentioned in Paragraph 1. It gives more details about what this process allows.
• Pair 2 (Paragraph 2 → Paragraph 3): Paragraph 3 connects with Paragraph 2 because it continues the topic of the float process. It explains how Pilkington was improving the process. This shows a logical order of ideas.
• Pair 3 (Paragraph 3 → Paragraph 4): Paragraph 4 connects with Paragraph 3 because it gives more details about the metal used in the process. It explains a requirement for the metal, which logically follows the discussion about Pilkington's idea.
• Pair 4 (Paragraph 4 → Paragraph 5): Paragraph 5 connects with Paragraph 4 because it answers the question of what metal is best for the process. It follows the logical order of discussing the requirements for the metal and then stating which metal is best.