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, which is about cups. It is a general statement that does not need any other sentence for context. It does not start with a conjunction or use pronouns. Why other lines are not chosen? Paragraph 2 starts with 'Its', which is a pronoun, so it cannot be independent. Paragraph 3 starts with 'Therefore', which is a conjunction, so it cannot be independent. Paragraph 4 also starts with 'Therefore', which is a conjunction, so it cannot be independent.

Concluding sentence: Why this is the last line? This paragraph is the last sentence because it wraps up the discussion about cups. It gives a conclusion about how the material choice is linked to the beverage. This shows that it summarizes the main points made in the previous paragraphs.

Paragraph pairs:

• Pair 1 (Paragraph 1 → Paragraph 2): Paragraph 2 connects with Paragraph 1 because it continues the topic of cups. The second sentence gives more details about the design of the cup. This shows a logical order from a general statement to a specific detail.
• Pair 2 (Paragraph 2 → Paragraph 3): Paragraph 3 connects with Paragraph 2 because it continues to talk about cups. After discussing the design, it moves to the material of the cup. This shows a logical order as it goes from one aspect of the cup to another.
• Pair 3 (Paragraph 3 → Paragraph 4): Paragraph 4 connects with Paragraph 3 because it explains why the material of the cup matters. It shows a cause and effect relationship, where the choice of material depends on the drink.