A.I. Explanation:

First sentence: Why this is the first line? This paragraph is the first sentence because it introduces the main topic of strength training. It clearly states why strength training is important. This follows the rule of Topic Sentence. Why other lines are not chosen? Paragraph 2 starts with "It" which is a pronoun, so it cannot be independent. Paragraph 3 starts with "Not only" which is a conjunction, so it cannot be independent. Paragraph 4 starts with "Conversely" which is also a conjunction, so it cannot be independent.

Concluding sentence: Why this is the last line? This paragraph is the last sentence because it wraps up the discussion by showing the negative effects of not doing strength training. It uses the word "Conversely" which signals a conclusion about the topic.

Paragraph pairs:

• Pair 1 (Paragraph 1 → Paragraph 2): Paragraph 2 connects with Paragraph 1 because it gives more details about strength training. This follows the Broader to Specific Strategy. Paragraph 1 talks about the importance of strength training, and Paragraph 2 explains how it is done.
• Pair 2 (Paragraph 2 → Paragraph 3): Paragraph 3 connects with Paragraph 2 because it adds more information about the benefits of strength training. This follows the Logical Order rule. Paragraph 2 explains what strength training is, and Paragraph 3 explains what it does.
• Pair 3 (Paragraph 3 → Paragraph 4): Paragraph 4 connects with Paragraph 3 because it shows the opposite side of not doing strength training. This follows the Contrast rule. Paragraph 3 talks about the benefits, and Paragraph 4 talks about the problems of not doing it.