First sentence: Why this is the first line? This paragraph is the first line because it introduces the main topic, which is Sir Edmund Halley. It gives a broad overview of who he is and what he is known for. This follows the rule of Topic Sentence. Why other lines are not chosen? Paragraph 2 starts with 'Yet one of his greatest accomplishments,' which makes it dependent on prior context. Paragraph 3 uses 'These variations,' which refers back to something not yet introduced. Paragraph 4 starts with 'Without it,' which also needs prior information to make sense.

Concluding sentence: Why this is the last line? This paragraph is the last line because it wraps up the discussion about Halley's work and its importance. It uses conclusive words like 'therefore impossible,' which signals the end of the topic. This follows the Conclusive Words rule.

Paragraph pairs:

• Pair 1 (Paragraph 1 → Paragraph 2): Paragraph 2 connects with Paragraph 1 because it continues to talk about Halley's accomplishments. This follows the Logical Order rule, as it shows what he is known for beyond the comet.
• Pair 2 (Paragraph 2 → Paragraph 3): Paragraph 3 connects with Paragraph 2 because it explains what the 'variations' are. This follows the Broader to Specific Strategy, as it gives more detail about the variations mentioned in Paragraph 2.
• Pair 3 (Paragraph 3 → Paragraph 4): Paragraph 4 connects with Paragraph 3 because it explains the importance of the variations. This follows the Cause and Effect Relationship rule, as it shows the effect of not knowing the declination.