A.I. Explanation:

First sentence: Why this is the first line? This paragraph is the first sentence because it introduces the main topic of starting a fitness journey. It gives a clear warning to consult a healthcare professional before starting. This follows the rule of Topic Sentence. Why other lines are not chosen? Paragraph 2 starts with 'Selecting', which is not independent. Paragraph 3 starts with 'With', which is a conjunction. Paragraph 4 starts with 'Keeping', which is not independent. All these sentences do not stand alone without context.

Concluding sentence: Why this is the last line? This paragraph is the last sentence because it wraps up the ideas by showing the importance of tracking progress. It summarizes the overall theme of maintaining motivation in a fitness journey.

Paragraph pairs:

• Pair 1 (Paragraph 1 → Paragraph 2): This pair connects because after consulting a healthcare professional, the next step is to select an exercise. This follows the Logical Order rule.
• Pair 2 (Paragraph 2 → Paragraph 3): This pair connects because after selecting an exercise, the next step is to create a schedule. This follows the Logical Order rule.
• Pair 3 (Paragraph 3 → Paragraph 4): This pair connects because after establishing a schedule, keeping a diary helps track progress. This follows the Cause and Effect Relationship rule.