A.I. Explanation:

First sentence: Why this is the first line? This paragraph is the first line because it introduces the main topic about keyboards and their design. It does not need any other sentence for context. It sets up the main idea without going into details. Why other lines are not chosen? Paragraph 2 starts with "Conversely," which is a conjunction. Paragraph 3 starts with "However," which is also a conjunction. Both of these cannot be first sentences. They need context from previous sentences. Therefore, they are not independent.

Concluding sentence: Why this is the last line? This paragraph is the last line because it wraps up the discussion about keyboards. It gives a final thought about the limitations of virtual keyboards.

Paragraph pairs:

• Pair 1 (Paragraph 1 → Paragraph 2): Paragraph 2 connects with Paragraph 1 because it gives more detail about the topic of keyboards. It explains what traditional keyboards are like, which supports the main idea.
• Pair 2 (Paragraph 2 → Paragraph 3): Paragraph 3 connects with Paragraph 2 because it contrasts traditional keyboards with modern devices. The word "Conversely" shows this contrast.
• Pair 3 (Paragraph 3 → Paragraph 4): Paragraph 4 connects with Paragraph 3 because it gives a downside to using virtual keyboards. The word "However" shows that it presents a different view.