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. It talks about the trend of keyboard customization. This is a broad overview of what the text will discuss. Why other lines are not chosen? The other paragraphs do not qualify as the first sentence. For example, Paragraph 2 starts with 'Users', which is a pronoun and needs context. Paragraph 3 starts with 'This personalization', which also uses a pronoun. Paragraph 4 starts with 'Nevertheless', which is a conjunction and shows a continuation of thought.

Concluding sentence: Why this is the last line? This paragraph is the last sentence because it wraps up the discussion by mentioning the challenges of customization. It gives a final thought on the topic.

Paragraph pairs:

• Pair 1 (Paragraph 1 → Paragraph 2): Paragraph 2 connects with Paragraph 1 because it gives specific examples of how users can customize their keyboards. This follows the Broader to Specific Strategy.
• Pair 2 (Paragraph 2 → Paragraph 3): Paragraph 3 connects with Paragraph 2 because it explains the benefits of the modifications mentioned in Paragraph 2. This follows the Logical Order strategy.
• Pair 3 (Paragraph 3 → Paragraph 4): Paragraph 4 connects with Paragraph 3 because it talks about the challenges of customization after discussing its benefits. This follows the Cause and Effect Relationship strategy.