A.I. Explanation:

First sentence: Why this is the first line? This paragraph is the first line because it introduces the main topic about the ocean floors. It does not refer to any previous information. It sets the stage for the discussion about the topography of the ocean floors. This follows the rule of Topic Sentence. Why other lines are not chosen? The other paragraphs are not chosen because they do not stand alone. For example, Paragraph 2 starts with "However," which is a conjunction. Paragraph 3 uses the definite article "the" which assumes prior knowledge. Paragraph 4 does not introduce a new topic and is more specific. Paragraph 5 also does not stand alone as it refers to previous ideas.

Concluding sentence: Why this is the last line? This paragraph is the last line because it summarizes the discussion about the ocean floors. It provides a final thought on the topic, showing how the ocean floors compare to land. This follows the rule of Summary Style.

Paragraph pairs:

• Pair 1 (Paragraph 1 → Paragraph 2): This pair connects because Paragraph 2 starts with "However," which shows a contrast to the idea in Paragraph 1. This follows the rule of Contrast.
• Pair 2 (Paragraph 2 → Paragraph 3): This pair connects because Paragraph 3 provides a specific example of the Atlantic floor mentioned in Paragraph 2. This follows the rule of Broader to Specific Strategy.
• Pair 3 (Paragraph 3 → Paragraph 4): This pair connects because Paragraph 4 continues the discussion about the Atlantic floor by mentioning other features. This follows the rule of Logical Order.
• Pair 4 (Paragraph 4 → Paragraph 5): This pair connects because Paragraph 5 gives more detail about the ruggedness of the ocean floors, which relates to the irregularities mentioned in Paragraph 4. This follows the rule of Topic Example.