First sentence: Why this is the first line? This paragraph is the first sentence because it introduces the main topic of glass cups. It does not refer to any previous information and gives a broad overview of the appeal of glass cups. This follows the rule of Topic Sentence. Why other lines are not chosen? The other paragraphs are not independent because: - Paragraph 2 starts with 'They', which is a pronoun referring back to 'glass cups'. - Paragraph 3 starts with 'However', which is a conjunction and shows a contrast. - Paragraph 4 starts with 'Thus', which is also a conjunction and indicates a conclusion.

Concluding sentence: Why this is the last line? This paragraph is the last sentence because it wraps up the discussion about glass cups. It gives a final thought on their suitability based on the earlier points. This follows the rule of Conclusive Words.

Paragraph pairs:

• Pair 1 (Paragraph 1 → Paragraph 2): Paragraph 2 connects with Paragraph 1 because it explains why glass cups are appealing. The phrase 'They allow the drinker to see the beverage' continues the idea of transparency from Paragraph 1. This follows the Logical Order rule.
• Pair 2 (Paragraph 2 → Paragraph 3): Paragraph 3 connects with Paragraph 2 because it introduces a contrast. The word 'However' shows that while glass cups are popular, they have a downside. This follows the Contrast rule.
• Pair 3 (Paragraph 3 → Paragraph 4): Paragraph 4 connects with Paragraph 3 because it gives a conclusion based on the previous information. The word 'Thus' shows that the suitability of glass cups is based on their poor insulation. This follows the Cause and Effect Relationship rule.