First sentence: Why this is the first line? This paragraph is the first line because it introduces the main topic of the text. It gives a broad overview of how the Earth was formed. It does not use any pronouns or definite articles that refer to previous information. This makes it independent and suitable as the opening sentence. Why other lines are not chosen? Paragraph 2 starts with "Initially," which is a transitional word, so it is not independent. Paragraph 3 starts with "Then," which also shows a continuation of thought. Paragraph 4 uses "the earth" which assumes prior knowledge. Paragraph 5 starts with "It," which is a pronoun and does not stand alone.

Concluding sentence: Why this is the last line? This paragraph is the last line because it wraps up the story of the Earth's formation. It shows the final result of the rain and how it contributed to forming seas. This gives closure to the overall theme.

Paragraph pairs:

• Pair 1 (Paragraph 1 → Paragraph 2): Paragraph 2 connects with Paragraph 1 because it continues the story of the Earth's formation. It uses the word "Initially" to show the order of events. This is a logical order.
• Pair 2 (Paragraph 2 → Paragraph 3): Paragraph 3 connects with Paragraph 2 because it follows the sequence of events. The word "Then" shows that this happens after the solid crust formed. This is a chronological order.
• Pair 3 (Paragraph 3 → Paragraph 4): Paragraph 4 connects with Paragraph 3 because it explains what happened after the rain formed. It logically follows the previous idea, showing a cause and effect relationship.
• Pair 4 (Paragraph 4 → Paragraph 5): Paragraph 5 connects with Paragraph 4 because it describes what happened after the rain fell. The word "It" refers back to the rain, showing a clear noun pronoun rule.