A.I. Explanation:

First sentence: Why this is the first line? This paragraph is the first sentence because it introduces the main topic of online education being cost-effective. It sets the stage for the discussion without needing prior context. This follows the rule of Topic Sentence. Why other lines are not chosen? The other paragraphs are not chosen because they do not stand alone. For example, Paragraph 2 starts with 'Reduced costs' which needs context. Paragraph 3 starts with 'Additionally' which is a conjunction. Paragraph 4 starts with 'However' which also indicates a continuation. Paragraph 5 starts with 'Institutions' which refers back to a subject not yet introduced.

Concluding sentence: Why this is the last line? This paragraph is the last sentence because it wraps up the discussion by explaining what is needed for effective online education. It provides a conclusion to the points made earlier.

Paragraph pairs:

• Pair 1 (Paragraph 1 → Paragraph 2): Paragraph 2 connects with Paragraph 1 because it provides specific examples of how online education is cost-effective. This follows the Broader to Specific Strategy.
• Pair 2 (Paragraph 2 → Paragraph 3): Paragraph 3 connects with Paragraph 2 because it adds more information about the benefits of online education. The word 'Additionally' shows a continuation of the idea, following the Connector Strategy.
• Pair 3 (Paragraph 3 → Paragraph 4): Paragraph 4 connects with Paragraph 3 because it presents a contrast. The word 'However' shows that while there are savings, there are also costs, following the Contrast rule.
• Pair 4 (Paragraph 4 → Paragraph 5): Paragraph 5 connects with Paragraph 4 because it explains what institutions need to do to manage the costs mentioned in Paragraph 4. This follows the Cause and Effect Relationship rule.