A.I. Explanation:

First sentence: Why this is the first line? This paragraph is the first line because it introduces the main topic about wild pandas. It gives a broad overview of the situation without needing other sentences for context. It does not use any pronouns or definite articles that refer to previous information. Why other lines are not choosen? The other paragraphs are not chosen because they do not stand alone. For example, Paragraph 2 starts with 'But', which is a conjunction. Paragraph 3 uses 'the' which assumes prior knowledge. Paragraph 4 and 5 also refer back to ideas in previous sentences.

Concluding sentence: Why this is the last line? This paragraph is the last line because it wraps up the discussion about pandas. It gives a conclusion about their interactions based on the findings. It summarizes the main points and reflects the overall theme of the text.

Paragraph pairs:

• Pair 1 (Paragraph 1 → Paragraph 2): This pair connects because Paragraph 2 gives specific information about what happened after we learned about the rarity of pandas. It uses the connector 'But' to show a change in the topic.
• Pair 2 (Paragraph 2 → Paragraph 3): This pair connects because Paragraph 3 explains what the collars did after they were attached. It follows a logical order where the action of attaching collars leads to the next step of tracking their positions.
• Pair 3 (Paragraph 3 → Paragraph 4): This pair connects because Paragraph 4 shows the results of the tracking. It explains what the team found based on the data from the collars, following a cause and effect relationship.
• Pair 4 (Paragraph 4 → Paragraph 5): This pair connects because Paragraph 5 gives an example of the findings in Paragraph 4. It uses the same theme of pandas being close to each other, showing a logical order from general findings to specific examples.