First sentence: Why this is the first line? This paragraph is the first sentence because it introduces the main topic about Plato. It gives a broad overview of who he was and his importance in mathematics. It does not need any other sentence for 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 'Inspired by Pythagoras', which needs context. Paragraph 3 starts with 'In particular', which also needs earlier information. Paragraph 4 starts with 'The sign above', which refers to something not yet mentioned.

Concluding sentence: Why this is the last line? This paragraph is the last sentence because it wraps up the ideas about Plato and his Academy. It gives a clear example of his views on geometry, which connects back to the main topic.

Paragraph pairs:

• Pair 1 (Paragraph 1 → Paragraph 2): Paragraph 2 connects to Paragraph 1 because it continues the topic of Plato's work in mathematics. It shows how he was inspired by Pythagoras, linking the two ideas.
• Pair 2 (Paragraph 2 → Paragraph 3): Paragraph 3 connects to Paragraph 2 because it gives more detail about Plato's beliefs. It explains that he thought geometry was very important, which follows from his work in mathematics.
• Pair 3 (Paragraph 3 → Paragraph 4): Paragraph 4 connects to Paragraph 3 because it gives an example of Plato's belief in geometry. The sign shows how important geometry was to him and his Academy.