First sentence: Why this is the first line? This paragraph is the first sentence because it introduces the main topic, which is Saturn and its rings. It does not need any other sentence for context. It gives a broad overview of Saturn's features. Why other lines are not chosen? The other paragraphs are not chosen because they do not stand alone. For example, Paragraph 2 starts with 'These rings,' which refers back to rings mentioned in the first sentence. Paragraph 3 starts with 'Scientists used to think,' which needs context from previous sentences. Paragraph 4 starts with 'Our knowledge,' which also needs prior information to make sense.

Concluding sentence: Why this is the last line? This paragraph is the last sentence because it wraps up the discussion about planets and their rings. It gives a summary of how our understanding has changed and what we might learn in the future. It uses conclusive words like 'we will probably find out more,' which signals the end of the text.

Paragraph pairs:

• Pair 1 (Paragraph 1 → Paragraph 2): Paragraph 2 connects to Paragraph 1 because it explains more about the rings mentioned in Paragraph 1. This is a 'Broader to Specific Strategy' where the first sentence gives a general idea about Saturn's rings, and the second sentence provides specific details about those rings.
• Pair 2 (Paragraph 2 → Paragraph 3): Paragraph 3 connects to Paragraph 2 because it introduces a new idea about rings in general. This is a 'Logical Order' where the second paragraph talks about the composition of the rings, and the third paragraph discusses the discovery of rings around other planets.
• Pair 3 (Paragraph 3 → Paragraph 4): Paragraph 4 connects to Paragraph 3 because it talks about the increase in knowledge about planets, which includes the discovery of rings. This is a 'Cause and Effect Relationship' where the discovery of rings leads to a broader understanding of planets.