A.I. Explanation:

First sentence: Why this is the first line? This paragraph is the first sentence because it introduces the main topic of mobility in Belgium before the railway. It does not need another sentence for context. It sets the stage for the discussion about transport. This follows the rule of Topic Sentence. Why other lines are not chosen? Paragraph 2 starts with 'Those who were wealthy', which uses a pronoun and refers back to a group, so it is not independent. Paragraph 3 starts with 'These travelled', which uses a pronoun that refers back to something mentioned before, so it is not independent. Paragraph 4 starts with 'As from the sixteenth century', which is not a general statement and does not stand alone, so it is not independent. Paragraph 5 starts with 'Until the invention of the iron track', which is not a general statement and does not stand alone, so it is not independent.

Concluding sentence: Why this is the last line? This paragraph is the last sentence because it wraps up the discussion about transport in Belgium. It summarizes the main point that tow barges were the best option before the railway. This follows the Summary Style rule.

Paragraph pairs:

• Pair 1 (Paragraph 1 → Paragraph 2): Paragraph 2 connects with Paragraph 1 because it continues the idea of mobility. It shows how wealthy people had better options for transport. This follows the Logical Order rule.
• Pair 2 (Paragraph 2 → Paragraph 3): Paragraph 3 connects with Paragraph 2 because it introduces another form of transport, the tow barges. This shows a Broader to Specific Strategy, moving from general transport options to a specific type.
• Pair 3 (Paragraph 3 → Paragraph 4): Paragraph 4 connects with Paragraph 3 because it gives more details about the tow barges. It explains how fast they travelled and their punctuality. This follows the Topic Example rule.
• Pair 4 (Paragraph 4 → Paragraph 5): Paragraph 5 connects with Paragraph 4 because it concludes the discussion about transport. It explains that before the railway, the tow barges were the best option. This follows the Logical Order rule.