A.I. Explanation:

First sentence: Why this is the first line? This paragraph is the first sentence because it introduces the main topic of exercise. It gives a broad overview of the idea that exercise is good for you. It does not refer to any previous information, so it stands alone. Why other lines are not chosen? Paragraph 2 starts with 'However,' which is a conjunction. Paragraph 3 starts with 'It is not all about,' which refers back to a previous idea. Paragraph 4 starts with 'On the contrary,' which also refers back. Paragraph 5 starts with 'For beginners,' which is specific and does not introduce the main topic.

Concluding sentence: Why this is the last line? This paragraph is the last sentence because it gives specific examples of exercise. It wraps up the ideas about exercise being good and enjoyable.

Paragraph pairs:

• Pair 1 (Paragraph 1 → Paragraph 2): Paragraph 2 connects with Paragraph 1 using the connector 'However.' This shows a contrast to the idea that exercise can be good without being hard.
• Pair 2 (Paragraph 2 → Paragraph 3): Paragraph 3 continues the idea from Paragraph 2. It explains that exercise does not have to be hard, and it gives examples of what it is not.
• Pair 3 (Paragraph 3 → Paragraph 4): Paragraph 4 connects with Paragraph 3 because it uses 'On the contrary.' This shows that exercising should be fun and not just hard work.
• Pair 4 (Paragraph 4 → Paragraph 5): Paragraph 5 links to Paragraph 4 by explaining what enjoyable exercise looks like. It gives specific examples of what beginners and advanced exercisers can do.