A.I. Explanation:

First sentence: Why this is the first line? This paragraph is the first sentence because it introduces the main topic of hacking into computer systems. It gives a clear example of a specific event that happened. This is an independent sentence because it can stand alone and does not need another sentence for context. It does not start with a conjunction or use pronouns that refer to previous ideas. Why other lines are not chosen? Paragraph 2 starts with "At first," which is a transitional phrase, so it is not independent. Paragraph 3 starts with "Any computer network," which is not general enough to stand alone. Paragraph 4 starts with "However," which is also a conjunction, making it not independent.

Concluding sentence: Why this is the last line? This paragraph is the last sentence because it wraps up the discussion about hacking and its dangers. It gives a clear conclusion about the potential for crime, which is the main theme of the text.

Paragraph pairs:

• Pair 1 (Paragraph 1 → Paragraph 2): This pair connects because Paragraph 2 explains the initial reaction to the hacking mentioned in Paragraph 1. The phrase "At first" shows a logical order of thought, moving from the event of hacking to the reaction to it.
• Pair 2 (Paragraph 2 → Paragraph 3): This pair connects because Paragraph 3 explains why the hacking was not serious. It shows a cause and effect relationship. The first paragraph talks about the fun aspect, and the next explains the vulnerability of networks.
• Pair 3 (Paragraph 3 → Paragraph 4): This pair connects because Paragraph 4 shows the serious side of hacking. It uses a broader to specific strategy. The first paragraph talks about general vulnerability, and the next gives specific examples of crime.