A.I. Explanation:

First sentence: Why this is the first line? This paragraph is the first sentence because it introduces the main topic of the text. It gives a broad overview of the tourism industry and its importance. 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 "It" which is a pronoun and needs context. Paragraph 3 starts with "Besides" which is a conjunction. Paragraph 4 starts with "Therefore" which also needs prior information.

Concluding sentence: Why this is the last line? This paragraph is the last sentence because it wraps up the main ideas of the text. It uses the phrase "Therefore" which signals a conclusion. This follows the Conclusive Words rule.

Paragraph pairs:

• Pair 1 (Paragraph 1 → Paragraph 2): Paragraph 2 connects with Paragraph 1 because it gives more details about the tourism industry. This follows the Broader to Specific Strategy. The first paragraph talks about the industry as a whole, and the second paragraph explains what sectors are included.
• Pair 2 (Paragraph 2 → Paragraph 3): Paragraph 3 connects with Paragraph 2 because it explains why the tourism industry is growing. This follows the Cause and Effect Relationship rule. The second paragraph talks about the sectors, and the third paragraph shows the reason for growth.
• Pair 3 (Paragraph 3 → Paragraph 4): Paragraph 4 connects with Paragraph 3 because it concludes the discussion about tourism's importance. This follows the Logical Order rule. The third paragraph explains growth, and the fourth paragraph shows the overall impact of tourism.