First sentence: Why this is the first line? This paragraph is the first line because it introduces the main topic of the text. It talks about the origin and evolution of main-belt comets, which is the main subject. 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 'Among the questions', which is a phrase that needs context. Paragraph 3 starts with 'Since only a few objects', which also needs prior information. Paragraph 4 starts with 'The various features', which assumes knowledge of 'features' and is not independent.

Concluding sentence: Why this is the last line? This paragraph is the last line because it wraps up the discussion about 288P. It summarizes the unique features of 288P, which relates back to the main topic. It provides closure to the text.

Paragraph pairs:

• Pair 1 (Paragraph 1 → Paragraph 2): Paragraph 2 connects to Paragraph 1 because it continues the discussion about main-belt comets. It uses the logical order rule, as it follows the introduction of the topic with a specific question related to it.
• Pair 2 (Paragraph 2 → Paragraph 3): Paragraph 3 connects to Paragraph 2 because it explains why the questions about main-belt comets are important. It uses the cause and effect relationship rule, as it shows the importance of studying these comets.
• Pair 3 (Paragraph 3 → Paragraph 4): Paragraph 4 connects to Paragraph 3 because it gives specific details about 288P. It uses the broader to specific strategy, as it starts with a general statement about the importance of 288P and then provides specific features.