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 tells us what topographic maps are and what they use. This is a general statement that does not need other sentences for context. It does not use any pronouns or definite articles that refer to previous ideas. Why other lines are not chosen? The other paragraphs are not chosen because they do not stand alone. For example, Paragraph 2 starts with "These lines," which refers back to the lines mentioned in Paragraph 1. Paragraph 3 starts with "The lines," which also refers back to the lines in Paragraph 1. Paragraph 4 starts with "If the numbers," which needs context from previous sentences. Therefore, they cannot be the first sentence.

Concluding sentence: Why this is the last line? This paragraph is the last sentence because it wraps up the information about contour lines and their numbers. It gives a specific conclusion about what the numbers mean. This helps to summarize the main points made in the previous paragraphs.

Paragraph pairs:

• Pair 1 (Paragraph 1 → Paragraph 2): Paragraph 2 connects with Paragraph 1 because it explains what the contour lines do. This is a logical order where the first paragraph gives a general idea, and the second paragraph gives more detail about those lines.
• Pair 2 (Paragraph 2 → Paragraph 3): Paragraph 3 connects with Paragraph 2 because it adds more information about the lines. It tells us that the lines have numbers, which helps us understand the elevation better. This shows a logical order from explaining the lines to giving details about them.
• Pair 3 (Paragraph 3 → Paragraph 4): Paragraph 4 connects with Paragraph 3 because it explains what happens with the numbers on the lines. It gives a specific example of how to read the numbers, which follows the general information in Paragraph 3. This shows a clear flow from general to specific.