A.I. Explanation:

First sentence: Why this is the first line? This paragraph is the first sentence because it introduces the main topic of digital marketing. It gives a broad overview of how digital marketing has changed sales methods. This follows the rule of Topic Sentence. Why other lines are not chosen? Paragraph 2 starts with "For instance," which is a transitional phrase. This means it cannot stand alone. Paragraph 3 uses "the advent of digital marketing" but it is not independent because it refers back to the topic. Paragraph 4 starts with "However," which is also a conjunction and cannot be the first sentence.

Concluding sentence: Why this is the last line? This paragraph is the last sentence because it wraps up the discussion. It shows the challenges of digital marketing after explaining its benefits. This follows the Conclusive Words rule.

Paragraph pairs:

• Pair 1 (Paragraph 1 → Paragraph 2): Paragraph 2 connects to Paragraph 1 because it gives an example of how digital marketing has changed sales methods. This follows the Broader to Specific Strategy.
• Pair 2 (Paragraph 2 → Paragraph 3): Paragraph 3 connects to Paragraph 2 because it adds more information about digital marketing. It continues the idea of online platforms with social media. This follows the Logical Order rule.
• Pair 3 (Paragraph 3 → Paragraph 4): Paragraph 4 connects to Paragraph 3 because it shows a contrast. While social media helps marketing, there are also challenges. This follows the Contrast rule.