First sentence: Why this is the first line? This paragraph is the first sentence because it introduces Pluto as a new topic. It gives a broad overview of Pluto's location and discovery. It does not refer to any previous information. Why other lines are not chosen? Paragraph 2 starts with "It has puzzled" which uses a pronoun and needs context. Paragraph 3 starts with "It's beyond doubt" which also uses a pronoun. Paragraph 4 starts with "Pluto has" which is not general. Paragraph 5 starts with "It receives" which uses a pronoun. Paragraph 6 starts with "Nevertheless" which is a conjunction.

Concluding sentence: Why this is the last line? This paragraph is the last sentence because it wraps up the discussion about Pluto. It shows that even with its cold temperature, Pluto still has interesting features. This gives a final thought about Pluto.

Paragraph pairs:

• Pair 1 (Paragraph 1 → Paragraph 2): Paragraph 2 connects to Paragraph 1 because it continues the discussion about Pluto. It shows how Pluto has made scientists think and argue about it. This is a logical order.
• Pair 2 (Paragraph 2 → Paragraph 3): Paragraph 3 connects to Paragraph 2 because it talks about Pluto being interesting. It follows the idea of scientists being puzzled by showing that Pluto has many new things to discover.
• Pair 3 (Paragraph 3 → Paragraph 4): Paragraph 4 connects to Paragraph 3 because it gives specific details about Pluto. After saying Pluto is fascinating, it explains why by mentioning its orbit and location.
• Pair 4 (Paragraph 4 → Paragraph 5): Paragraph 5 connects to Paragraph 4 because it gives more information about Pluto's environment. After talking about its orbit, it explains how the orbit affects its temperature.
• Pair 5 (Paragraph 5 → Paragraph 6): Paragraph 6 connects to Paragraph 5 because it introduces new information about Pluto's surface. After discussing the cold temperature, it shows that there is still activity on Pluto.