First sentence: Why this is the first line? This paragraph is the first line because it introduces the main topic, which is the 'one chip' challenge. It gives a clear overview of what the challenge is and its effects on students. It does not use any pronouns or definite articles that refer to previous information. Why other lines are not chosen? Paragraph 2 starts with 'It's', which is a pronoun and does not stand alone. Paragraph 3 starts with 'Others', which refers back to something not mentioned yet. Paragraph 4 starts with 'Some challenges', which also refers to previous ideas. All these reasons make them not independent.

Concluding sentence: Why this is the last line? This paragraph is the last line because it concludes the discussion about different types of challenges. It does not introduce new ideas but wraps up the topic by showing another kind of challenge.

Paragraph pairs:

• Pair 1 (Paragraph 1 → Paragraph 2): Paragraph 2 connects to Paragraph 1 because it uses the connector 'It's' to show that the 'one chip' challenge is part of a larger trend of viral challenges. This shows a logical order of ideas.
• Pair 2 (Paragraph 2 → Paragraph 3): Paragraph 3 connects to Paragraph 2 because it gives a specific example of the viral challenges mentioned in Paragraph 2. This follows the broader to specific strategy.
• Pair 3 (Paragraph 3 → Paragraph 4): Paragraph 4 connects to Paragraph 3 because it introduces another type of challenge. The word 'Others' shows a contrast between the challenges that involve consumption and those that are daredevil-oriented.