A.I. Explanation:

First sentence: Why this is the first line? This paragraph is the first sentence because it introduces the main topic of sharks and their long history. It is a general statement that does not need other sentences for context. It sets the stage for the following information about sharks. Why other lines are not chosen? The other paragraphs are not chosen because they do not stand alone. For example, Paragraph 2 starts with 'They', which is a pronoun that refers back to sharks, so it cannot be first. Paragraph 3 starts with 'However', which is a conjunction, so it cannot be first. Paragraph 4 starts with 'Consequently', which is also a conjunction, so it cannot be first.

Concluding sentence: Why this is the last line? This paragraph is the last sentence because it wraps up the information about sharks. It gives a final thought on how their adaptation helps them in water. The word 'Consequently' signals that this is the conclusion of the ideas presented.

Paragraph pairs:

• Pair 1 (Paragraph 1 → Paragraph 2): Paragraph 2 connects to Paragraph 1 because it continues the topic of sharks. The phrase 'They are found' refers back to sharks, showing a logical flow of ideas.
• Pair 2 (Paragraph 2 → Paragraph 3): Paragraph 3 connects to Paragraph 2 because it introduces a contrast. The word 'However' shows that there is a difference between sharks and most fish, linking the two ideas.
• Pair 3 (Paragraph 3 → Paragraph 4): Paragraph 4 connects to Paragraph 3 because it explains the effect of having cartilage instead of bone. The word 'Consequently' shows that the flexibility and agility are a result of the previous information.