First sentence: Why this is the first line? This paragraph is the first line because it introduces the main topic. It tells us about a team of scientists and their discovery. This is a general statement that does not need other sentences for context. It does not start with a conjunction or use pronouns. Why other lines are not chosen? Paragraph 2 starts with 'Using' which is a conjunction. Paragraph 3 starts with 'Four' which is not general. Paragraph 4 starts with 'These' which refers back to something, so it is not independent.

Concluding sentence: Why this is the last line? This paragraph is the last line because it summarizes the details about the super-Earths. It gives specific information about their sizes. This wraps up the main topic of the paragraph.

Paragraph pairs:

• Pair 1 (Paragraph 1 → Paragraph 2): Paragraph 2 connects to Paragraph 1 because it continues the story of the team of scientists. The phrase 'Using observations' shows how they found the planets. This is a logical order.
• Pair 2 (Paragraph 2 → Paragraph 3): Paragraph 3 connects to Paragraph 2 because it gives more details about the planets found. The phrase 'Four of these planets' shows that it is talking about the planets mentioned in the previous paragraph. This is a broader to specific strategy.
• Pair 3 (Paragraph 3 → Paragraph 4): Paragraph 4 connects to Paragraph 3 because it gives specific measurements of the super-Earths mentioned. The phrase 'These new super-Earths' refers back to the super-Earths in the previous paragraph. This is a noun pronoun rule.